Class 10th Science Gujarat Board Solution
Exercise- The direction of magnetic field lines in a region outside the bar magnet is ______A. From…
- Which of the following statements is false?A. The direction of magnetic field lines is…
- By which instrument the presence of a magnetic field can be determined?A. Voltmeter B.…
- Who had first observed the magnetic effect of an electric current?A. Faraday B. Oersted C.…
- With the help of which law the direction of a magnetic field can be decided?A. Faraday’s…
- According to right-hand thumb rule, whose direction is indicated by a thumb?A. Electric…
- The magnetic field produced in a straight wire on passing the current through it is…
- What is the field line of a magnetic field passing through the centre of current carrying…
- Whose magnetic field is like a magnetic field of a bar magnet?A. Current carrying wire B.…
- Who gave the principle of electromagnetic induction?A. Faraday B. Oersted C. Ampere D.…
- Which is the direction of the magnetic force acting on a current carrying wire placed in a…
- How is a current carrying wire placed in a magnetic field so that magnetic field does not…
- From which of the following cases, the induced current in the loop will not be obtained?A.…
- Which instrument is used in converting electrical energy into mechanical energy?A.…
- On which principle does the electric generator work?A. Electrical energy is converted into…
- The magnitude of an AC voltage used in India is _________ and the frequency is _____.A.…
- Which coloured wire is used for earthing?A. Red B. Black C. Green D. Can be of any colour.…
- Which type of current is obtained from a battery?A. DC current B. AC current C. Voltmeter…
- Which instrument is used to know the presence of an electric current?A. Fuse B.…
- A fuse wire is _______________A. conductor B. insulator C. semiconductor D. made up of any…
- __________ rule is used to know the direction of an induced current in the circuit.A.…
- How many times does an AC electric current with the frequency 50Hz change its direction?A.…
- At the centre of which of the following four circular rings has maximum magnetic field…
- Give the characteristic of magnetic field lines.
- Explain the ‘right hand thumb rule’ to know the direction of magnetic field.…
- What will happen while placing a current conductor in a magnetic field? Explain.…
- By which law can the direction of an induced electric current can be determined? Give the…
- Explain the provision of the earthing wire.
- Mention the usefulness of a fuse in a domestic electrical circuit.…
- Discuss the magnetic field resulting from a current carrying circular ring.…
- What is solenoid? Give the characteristics of magnet from solenoid.…
- What precautions should be taken during the use of electricity?
- Describe the experiment that explains the phenomenon of an electromagnetic induction and…
- Write a short note on electric bell.
- Describe domestic electric circuit with the help of a diagram.
- Describe the principle, construction and working of an electric motor along with a figure.…
- Describe the principle, construction and working of an electric generator with a figure.…
- The direction of magnetic field lines in a region outside the bar magnet is ______A. From…
- Which of the following statements is false?A. The direction of magnetic field lines is…
- By which instrument the presence of a magnetic field can be determined?A. Voltmeter B.…
- Who had first observed the magnetic effect of an electric current?A. Faraday B. Oersted C.…
- With the help of which law the direction of a magnetic field can be decided?A. Faraday’s…
- According to right-hand thumb rule, whose direction is indicated by a thumb?A. Electric…
- The magnetic field produced in a straight wire on passing the current through it is…
- What is the field line of a magnetic field passing through the centre of current carrying…
- Whose magnetic field is like a magnetic field of a bar magnet?A. Current carrying wire B.…
- Who gave the principle of electromagnetic induction?A. Faraday B. Oersted C. Ampere D.…
- Which is the direction of the magnetic force acting on a current carrying wire placed in a…
- How is a current carrying wire placed in a magnetic field so that magnetic field does not…
- From which of the following cases, the induced current in the loop will not be obtained?A.…
- Which instrument is used in converting electrical energy into mechanical energy?A.…
- On which principle does the electric generator work?A. Electrical energy is converted into…
- The magnitude of an AC voltage used in India is _________ and the frequency is _____.A.…
- Which coloured wire is used for earthing?A. Red B. Black C. Green D. Can be of any colour.…
- Which type of current is obtained from a battery?A. DC current B. AC current C. Voltmeter…
- Which instrument is used to know the presence of an electric current?A. Fuse B.…
- A fuse wire is _______________A. conductor B. insulator C. semiconductor D. made up of any…
- __________ rule is used to know the direction of an induced current in the circuit.A.…
- How many times does an AC electric current with the frequency 50Hz change its direction?A.…
- At the centre of which of the following four circular rings has maximum magnetic field…
- Give the characteristic of magnetic field lines.
- Explain the ‘right hand thumb rule’ to know the direction of magnetic field.…
- What will happen while placing a current conductor in a magnetic field? Explain.…
- By which law can the direction of an induced electric current can be determined? Give the…
- Explain the provision of the earthing wire.
- Mention the usefulness of a fuse in a domestic electrical circuit.…
- Discuss the magnetic field resulting from a current carrying circular ring.…
- What is solenoid? Give the characteristics of magnet from solenoid.…
- What precautions should be taken during the use of electricity?
- Describe the experiment that explains the phenomenon of an electromagnetic induction and…
- Write a short note on electric bell.
- Describe domestic electric circuit with the help of a diagram.
- Describe the principle, construction and working of an electric motor along with a figure.…
- Describe the principle, construction and working of an electric generator with a figure.…
Exercise
Question 1.The direction of magnetic field lines in a region outside the bar magnet is ______
A. From the N pole towards the S pole of a magnet.
B. From the S pole towards the N pole of a magnet.
C. In the direction coming out from both the poles of a magnet.
D. In the direction entering in both the poles of a magnet.
Answer:As we know magnetic field lines always form closed loop. Inside the magnet the direction of magnetic field lines is from South Pole of the magnet to the North Pole of the magnet. But when the magnetic field lines come out of the North Pole, they have to form a closed loop, so they turn in outside region to go back to the South Pole. Hence, that is why direction of magnetic field lines in a region outside the bar magnet from the N pole towards the S pole of a magnet.
Question 2.Which of the following statements is false?
A. The direction of magnetic field lines is from N to S.
B. In the region where the magnetic field lines are at a close distance from each other, there will be a strong magnetic field.
C. The magnetic field lines form closed loops.
D. The magnetic field lines can cross each other.
Answer:According to statement A, the direction of the magnetic field line is from N to S, which is true.
According to statement B closer the magnetic field lines stronger the magnetic field there. We can think it like magnetic field lines are very close to each other near the magnetic bar. But as we go far away they also start separating and show weak magnetic field.
According to statement C magnetic field lines always form close loop. They can never have loose ends. They always start from a pole and end up on the other pole.
But according to statement D magnetic field lines can cross each other, which is wrong. Magnetic field lines always form close loop. And at any point, magnetic field always have a certain direction but if magnetic field lines cross each other, that will result into two directions of a magnetic field on a single point which is impossible.
Question 3.By which instrument the presence of a magnetic field can be determined?
A. Voltmeter
B. Ammeter
C. Galvanometer
D. Magnetic needle.
Answer:Voltmeter is a device which is used to measure the voltage in a circuit.
Similarly, Ammeter and Galvanometer are devices which are used to measure the current in a circuit.
But the Magnetic needle is an object which has its own natural magnetism. We do not have to connect it any circuit to start its magnetic properties. The presence of that magnetism will disturb the magnetic field present and there will be a force on the magnetic needle which will cause its movement. And that is how magnetic needle detects the presence of magnetic field.
Question 4.Who had first observed the magnetic effect of an electric current?
A. Faraday
B. Oersted
C. Volta
D. Ampere.
Answer:Oersted was a Danish physicist and chemist who discovered that electric currents create magnetic fields, which was the first connection found between electricity and magnetism. He noticed it when a compass needle is deflected when an electric current from a battery was switched on and off, confirming a direct relationship between electricity and magnetism.
While Faraday gives the concept of induction, Volta invented the battery and Ampere found about the current.
Question 5.With the help of which law the direction of a magnetic field can be decided?
A. Faraday’s law
B. Fleming’s right-hand rule
C. Right-hand thumb rule
D. Fleming’s left-hand rule
Answer:According to Right-hand thumb rule when we arrange our right-hand thumb in the direction of the current and as we wrap our finger around the current carrying conductor, the wrapped finger will show the direction of the magnetic current. This law helps in finding the direction of the magnetic field from a current carrying conductor. This law also implies that magnetic field and current will always be perpendicular.
While Fleming’s right-hand rule helps to find out the direction of the induced magnetic current. And Fleming’s left-hand rule helps to find out the direction of the magnetic force.
Question 6.According to right-hand thumb rule, whose direction is indicated by a thumb?
A. Electric current
B. Magnetic field
C. Magnetic force
D. Motion of a conductor
Answer:According to Right-hand thumb rule when we arrange our right hand's thumb in the direction of the current and as we wrap our finger around the current carrying conductor, the wrapped finger will show the direction of the magnetic field.
Hence, the thumb denotes the direction of current.
Question 7.The magnetic field produced in a straight wire on passing the current through it is ______
A. in the direction of current
B. in the direction opposite to the current.
C. circular around the wire
D. in the direction parallel to the wire.
Answer:The direction of the induced magnetic field from a current carrying conductor is given by the Right-hand thumb rule. According to Right-hand thumb rule when we arrange our right hand's thumb in the direction of the current and as we wrap our finger around the current carrying conductor, the wrapped finger will show the direction of the magnetic field.
So, that will result into a Circular ring around the wire.
Question 8.What is the field line of a magnetic field passing through the centre of current carrying circular ring?
A. Circular
B. Straight line
C. Ellipse
D. The magnetic field is zero at the centre.
Answer:The direction of the induced magnetic field from a current carrying conductor is given by The Right-hand thumb rule. In a case of a current carrying circular ring, we first divide the ring into various small parts and then we will see the contribution of each part.
First, consider the leftmost part which has a magnetic field which is coming out of the paper i.e. perpendicular to the paper. Similarly, when we consider the rightmost part whose magnetic field is also coming out of the paper and also perpendicular to the paper. So, while coming from left to right all the parts will contribute their magnetic fields similarly. And the resultant magnetic field at the center of the ring is coming out of the paper and perpendicular to the paper.
(In the figure we have to consider wire lying on a paper)
Now it is obvious that the ring lines are circular near the wire but when we come away from the wire they change and they approximately result into straight lines near the center of the ring because as distance increase the radius of the magnetic circle increase. Which is shown in the picture below:-
That is why the magnetic field lines are straight near the center of the current carrying circular ring.
Question 9.Whose magnetic field is like a magnetic field of a bar magnet?
A. Current carrying wire
B. Current carrying ring.
C. Current carrying solenoid
D. Current carrying rectangular loop
Answer:The magnetic field of a bar magnet is shown in the first figure. In which we can see inside the magnet the direction of the magnetic field is from the South Pole to the North Pole. But outside the magnet it is from North to the South Pole, it is because magnetic field always forms close loop.
A solenoid is a device which is formed when an insulated current-carrying wire is bent into a coil with N number of loops or turns. It is like the wrapping of a wire on a cylindrical object. The individual magnetic field of each turn contribute and it results in a magnetic field which is like the magnetic field of a bar magnet. The direction of the magnetic field inside the solenoid is determined by Right-hand thumb rule. That is, the magnetic field inside the solenoid is directed from south to north but outside the solenoid, it is from North to South, which are a similar magnetic field like a bar magnet.
Question 10.Who gave the principle of electromagnetic induction?
A. Faraday
B. Oersted
C. Ampere
D. Volta
Answer:Michael Faraday was a scientist who contributed to the study of electromagnetism. His main discoveries include the underlying electromagnetic induction, diamagnetism, and electrolysis. His breakthrough came when he wrapped two insulated coils of wire around an iron ring and found that upon passing a current through one coil a momentary current was induced in the other coil. This phenomenon is now known as induction. In subsequent experiments, he found that if he moved a magnet through a loop of wire an electric current flowed in that wire. The current also flowed if the loop was moved over a stationary magnet.
Question 11.Which is the direction of the magnetic force acting on a current carrying wire placed in a magnetic field?
A. along magnetic field
B. along the electric current
C. perpendicular to the magnetic field
D. opposite to magnetic field.
Answer:The direction of the magnetic force acting on a current wire placed in a magnetic field is given by Fleming’s left hands rule.
According to Fleming’s Left-hand rule: - If we arrange our left hand's thumb, index finger and middle finger mutually perpendicular to each other. And if we put our index finger in the direction of magnetic field applied and center finger in direction of electric current then the thumb will point in the direction of the magnetic force.
So, as mentioned magnetic force, magnetic field and electric current all are perpendicular to each other.
Question 12.How is a current carrying wire placed in a magnetic field so that magnetic field does not act on it?
A. Parallel to magnetic field
B. Perpendicular to magnetic field.
C. At an angle 40o with the magnetic field
D. Can be arranged anyway.
Answer:When the current carrying wire is placed parallel or anti-parallel to the magnetic field then and only then the magnetic field does not act on it.
The magnetic force depends on four things:
•Amount of current
•The strength of Magnetic field
•Length of the wire which remain in the magnetic field
•And the angle between the current carrying conductor and magnetic field.
The most important criteria here is the angle between the current carrying conductor and the magnetic field. If the angle is 0° or 180° then there will be no force acting on the wire. But if the angle is 90° the force will be maximum. If you observe the pattern it goes on like that, at 0° the force is 0 but as the angle increases the force increases and at 90° the force reaches its maximum value. And then again it starts decreasing and it becomes 0 at 180°.
Question 13.From which of the following cases, the induced current in the loop will not be obtained?
A. The loop is moved in the direction of the magnet.
B. The magnet is moved in the direction of the loop.
C. The loop and magnet are moved in the opposite directions with the same speed.
D. The loop and magnet are moved in one direction with the same speed.
Answer:The current will only induce in the coil if the magnetic field around the coil changes. This can only happen when:
•Magnet move towards the coil or move away from it.
•Coil move toward the magnet or move away from it.
•Both move towards each other {or we can also say loop and magnet move in opposite direction with same speed.}
These five condition are the only condition for induction of current in the loop.
But, in option D the magnet and loop are moving in one direction let's say positive X-axis with same speed. Such movement will not change the magnetic field between them because the distance between them is also constant.
So, option A, B, C will result into induction of current but option D won't.
Question 14.Which instrument is used in converting electrical energy into mechanical energy?
A. Electric generator
B. Electric motor
C. Electric iron
D. Electric oven
Answer:An Electric motor converts electrical energy into mechanical energy. The main point here to note is that a current has its magnetic field. Working:-
•Inside the motor there is a conductor wire placed between fixed strong magnets.
•When current is provided to the electric motor the wire inside the motor get magnetised due to flow of current.
•These wires are already placed in strong magnetic field of a strong magnet.
•This cause a repulsion between the wire and the strong magnets. This repulsion cause movement of wire. The direction of movement is determined by Fleming's left hand rule.
Electric motor is use for doing very mechanical works. It has a very widespread application like in fan, car, etc.
Question 15.On which principle does the electric generator work?
A. Electrical energy is converted into mechanical energy.
B. Electrical energy is converted into thermal energy.
C. Mechanical energy is converted into electrical energy.
D. Electrical energy is converted into light energy.
Answer:Electric generator is a device which converts mechanical work into electrical energy. The main point here to note is that a changing magnetic field can induce current in a conductor. Working of the generator:
•Inside the generator there is a conductor wire placed between fixed strong magnets.
•When mechanical rotation is provided to that wire the magnetic field associated with the wire changes.
•Those wire are already placed in strong magnetic field of a strong magnet.
•So, the motion of the wire changes the magnetic field and induce an electric current in the wire.
•The direction of induced current is determined by Fleming's right hand rule.
Question 16.The magnitude of an AC voltage used in India is _________ and the frequency is _____.
A. 110 V, 60Hz
B. 110V, 50Hz
C. 220V, 50Hz
D. 220V, 60HZ
Answer:Frequency of an AC current implies number of complete wave present in a second. 50 hertz frequency means that there are 50 waves present in an interval of one second.
Most of the houses in India are provided with 220 V voltage and it is further modified according to the voltage requirement of the devices.
Question 17.Which coloured wire is used for earthing?
A. Red
B. Black
C. Green
D. Can be of any colour.
Answer:Basically earthing wire is the safety measure to prevent shocks and device damages. Devices like electric motor, heater, iron and refrigerator use very high amount of current. Whenever there is a leak of electricity/current from these devices, the leaked current reaches the metallic plates of these devices and if we touch them with bare hand we will get a shock. This may cause very harmful damage.
So, to prevent such type of situation there is earthing wire, which basically absorb all the leaked current from the device and dump it to the earth. This dumping of leaked current from the device is very useful as it prevents damage to the device as well as human.
Question 18.Which type of current is obtained from a battery?
A. DC current
B. AC current
C. Voltmeter
D. Magnetic needle
Answer:A battery is a source to Direct Current (DC). It provide a constant value of current which does not change with the time. This is because in a battery there are two terminal one positive and one negative and the current flows only from positive terminal to the negative terminal. It flows in one direction only that is from positive to negative which is the characteristic of DC current. Hence, that is why battery is source of DC current.
If the current varies its value that is positive to negative and negative to positive then the current is said to be Alternating Current (AC).
Question 19.Which instrument is used to know the presence of an electric current?
A. Fuse
B. Galvanometer
C. Voltmeter
D. Magnetic needle
Answer:Galvanometer is a very sensitive device which measures the amount of current as well as the direction of current. From the Induction of Current experiment we see that the induced current changes its direction when we move magnet towards the coil and when we move away from it. It is a sensitive device so it is mainly use to find out the presence of current rather than the amount of current.
While Voltmeter is used to measure voltage, magnetic needle is used to find out the presence of magnetic field and fuse is for safety purposes in an electric circuit.
Question 20.A fuse wire is _______________
A. conductor
B. insulator
C. semiconductor
D. made up of any material
Answer:A fuse wire is basically a safety measure to prevent electric fires and short circuits. Fuse wire is a conductor wire with a very low melting point. Low melting point is the main characteristic here.
•Some devices require very high amount of current, the flow of so much current can sometime cause the melting of the insulating wire due to heating effect of the electric current.
•This can result into severe electric fires. To prevent these situation a fuse is introduced into the circuit, which is made up of a low melting point conductor wire.
•The wire inside the conductor melts and breaks the circuit as soon as the heating due to current increases.
This prevents further fire or electric short circuit.
Question 21.__________ rule is used to know the direction of an induced current in the circuit.
A. Fleming’s left hand
B. Fleming’s right hand
C. Right hand thumb
D. Ampere's
Answer:As we know from Faraday's law that a current induces in a conductor whenever conductor is moving through a magnetic field.
Fleming' right hand rule is use to find out the direction of the induced current within a conductor, when the conductor is moving in a magnetic field.
•According to the Fleming’s right hand rule, if we put our thumb, index finger and middle finger mutually perpendicular to each other.
•Such that thumb points in the direction of the motion of conductor and index finger point in the direction of the applied magnetic field. The given picture illustrates the rule:
•Then middle/centre finger will show the direction of the induced or generated current within the conductor.
Question 22.How many times does an AC electric current with the frequency 50Hz change its direction?
A. 25
B. 50
C. 100
D. 200
Answer:To answer the question we have to first understand it. Frequency of an AC current implies number of complete wave present in a second. 50 hertz frequency means that there are 50 waves present in an interval of one second. The given picture will clear all he doubt,
In the picture there is only one complete wave in a second, hence its frequency is 1 hertz. Also observe that in one wave the current change its direction twice first positive than negative.
Now, if the frequency of the current is 50 hertz, which means that there are 50 such waves present in one second and then the current will change its direction 100 times.
Question 23.At the centre of which of the following four circular rings has maximum magnetic field while passing equal current through each one?
A. 
B. 
C. 
D. 
Answer:The direction of the induced magnetic field from a current carrying conductor is given by the Right hand thumb rule. In a case of a current carrying circular ring, magnetic field at the centre of the ring is coming out of the paper and perpendicular to the paper.
Now it is obvious that the magnetic field is stronger near the wire but when we come away from the wire it weakens and at the centre of the ring it is weakest. Hence, more the radius the ring the more magnetic field is weak at centre of the ring.
So, (d) will have the weakest magnetic field at centre and (a) has the strongest magnetic field at centre.
Question 24.Give the characteristic of magnetic field lines.
Answer:Following are some characteristics of the magnetic field lines:
•The direction of magnetic field inside the magnet is from S to N. Which we have observed, but outside the magnet the direction of magnetic field lines is from North to South, the reason behind that is the next characteristic.
•Magnetic field lines always form close loop. They can never have loose ends. They always start from a pole and end up on another pole. This characteristic is the most important characteristic this is also the reason behind why outside the magnet the direction of field line is north to south.
•Closure the magnetic field lines stronger the magnetic field there is. We can think it like magnetic field lines are very close to each other near the magnetic bar. But as we go far away they also start separating and show weak magnetic field.
•Magnetic field lines can never cross each other. Magnetic field lines always form close loop. And any point in a magnetic field always a certain direction but if magnetic field lines cross each other, that will result into two direction of a magnetic field on a single point which is impossible.
Question 25.Explain the ‘right hand thumb rule’ to know the direction of magnetic field.
Answer:The direction of the induced magnetic field from a current carrying conductor is given by the Right hand thumb rule. According to Right hand thumb rule:-
•When we place our right hand's thumb in the direction of the current and as we wrap our finger around the current carrying conductor.
•Wrapped finger will show the direction of the magnetic field.
•It is noticeable that the wrapped finger from a close loop which is the most important property of the magnetic field.
Hence, when we place our right hand's thumb in the direction of the current carrying wire the circular rings formed by our finger will denote the magnetic field.
Question 26.What will happen while placing a current conductor in a magnetic field? Explain.
Answer:Whenever a current carrying conductor is placed in a magnetic field then the conductor will experience a magnetic force. This happen because the current in the conductor has its own magnetic field and there is also a magnetic field present. So both the field will interact and will result in repulsion or attraction of the conductor wire toward the fixed magnets.
The magnetic force depend on four things:
•Amount of current
•Strength of Magnetic field
•Length of the wire which remain in magnetic field
•And the angle between the current carrying conductor and magnetic field.
The direction of magnetic force acting on a current wire placed in a magnetic field is given by Fleming’s left hands rule.
Question 27.By which law can the direction of an induced electric current can be determined? Give the explanation of the law.
Answer:Fleming' right hand rule is use to find out the direction of the induced current within a conductor. As we know from Faraday's law that a current induces in a conductor whenever conductor is moving through a magnetic field.
So, according to the Fleming’s right hand rule,
•If we put our thumb, index finger and middle finger mutually perpendicular to each other. As shown in the picture.
•Such that thumb points in the direction of the motion of conductor and index finger point in the direction of the applied magnetic field.
•Then middle/centre finger will show the direction of the induced or generated current within the conductor.
Question 28.Explain the provision of the earthing wire.
Answer:Basically earthing wire is the safety measure to prevent shocks and device damage. The following points will clarify:
•Devices like electric motor, heater, iron and refrigerator use very high amount of current.
•So sometimes, there is a leak of electricity/current from these devices, the leaked current reaches the metallic plates present under these devices and if we touch such devices with bare hand we will get a shock. This may cause very harmful damage.
•So, to prevent such type of situation there is earthing wire, which basically absorb all the leaked current from the device and dump it to the earth. As, earthing wire is connected between metallic plates of device and earth. Earth then absorb all the leaked current and prevent us from any danger.
This dumping of leaked current from the device is very useful as it prevents damage to the device as well as human.
Question 29.Mention the usefulness of a fuse in a domestic electrical circuit.
Answer:A fuse wire is a safety measure to prevent electric fires and short circuits. Some usefulness of Fuse:
•Without using Fuse we will be facing daily short circuited electric circuits.
•Device which require high current can damage permanently causing loss of money and resources.
•Also, fuse prevents electric fires.
Basically, Fuse wire is a conductor wire with a very low melting point. Low melting point is the main characteristic here. Working of fuse wire:
•Some devices require very high amount of current, the flow of so much current can sometime cause the melting of the insulating wire due to heating effect of the electric current.
•This can result into severe electric fires. To prevent these situation a fuse is introduced into the circuit, which is made up of a low melting point conductor wire.
•The wire inside the conductor melts and breaks the circuit as soon as the heating due to current increases.
This prevents further fire or electric short circuit.
Question 30.Discuss the magnetic field resulting from a current carrying circular ring.
Answer:In a case of a current carrying circular ring, we first divide the ring into various small parts and then we will see contribution of each part.
•First consider the leftmost part which have a magnetic field which is coming out of the paper i.e. perpendicular to the paper.
•Similarly, when we consider the rightmost part whose magnetic field is also coming out of the paper and also perpendicular to the paper.
•So, while coming from left to right all the parts will contribute their magnetic fields similarly. And the resultant magnetic field at the centre of the ring is coming out of the paper and perpendicular to the paper.
(The resultant magnetic field of the ring.)
Now it is obvious that the ring lines are circular near the wire but when we come away from the wire they change and they nearly convert into straight lines near the centre of the ring because the radius of the magnetic circle increase as we move towards the centre of the ring which result into the straight light of magnetic field lines.
Question 31.What is solenoid? Give the characteristics of magnet from solenoid.
Answer:A solenoid is a device which is formed when an insulated current carrying wire is bent into a coil with an N number of loops or turns. It is like wrapping of a wire on a cylindrical object.
•The individual magnetic field of each turn contribute and it results into a magnetic field which is like the magnetic field of a bar magnet.
•The magnetic field of the solenoid depend on the number of turns present. It is directly proportional to the number of turns, ore number of turns more strong magnetism. For example if we have to lift a very have metal pipe we would use a solenoid with very large number of turns, as they will have a stronger magnetic field. In simple terms the magnetism of a solenoid is controllable.
•Furthermore the magnetism of a solenoid can be increased by putting an iron rod through the coils.
•The direction of that magnetic field inside the solenoid is determined by Right hand thumb rule which is directed from south to north but outside the solenoid it is from North to South.
Question 32.What precautions should be taken during the use of electricity?
Answer:Electricity is as dangerous as it is useful, in dealing with electricity or electric device one must be very careful. Carelessness may even cause death. There is no escape from it. We use electricity in our household and daily life, here are some precautions we should do to prevent any kind of loss:
1. Always use appropriate insulated rubber gloves and goggles while working on any branch circuit or any other electrical circuit.
2. Avoid water at all times when working with electricity. Never touch or try repairing any electrical equipment or circuits with wet hands.
3. Never use any electrical device with broken cords, damaged insulation or broken plugs.
4. Do not touch anything without complete knowledge. This may cause severe damage.
5. Follow the safety rules established by the companies of the device which you are handling.
6. Never use an aluminium or steel ladder if you are working on any receptacle at height in your home. Use a bamboo, wooden or a fibreglass ladder instead.
7. Always wear rubber slippers/shoes while handling electricity.
Question 33.Describe the experiment that explains the phenomenon of an electromagnetic induction and give its conclusion.
Answer:The experiment was first done by Michael Faraday. He observed that the current will only induce in the coil if the magnetic field around the coil changes.
In the experiment, he first made a loop of conducting wire and connect a galvanometer with it to record the observation. Then he performed the following things and recorded observation in each case:
•He move a magnet towards the coil or move away from it.
•He made an observation also when both are stationary.
•Then he moved the Coil toward the magnet or move away from it.
•Then he move both of them towards each other.
Result of the experiment: From the observation he concluded that whenever the magnetic field around a conductor wire changes it produces current in the wire. His first, second and third observation resulted in a deflection produced in the galvanometer because as the coil or magnet moves the magnetic field changes. But in the second observation both of them were steady which results in no induction current.
Conclusion of the experiment: He finally concluded that whenever magnetic field around a conductor wire changes, results in induction of the current.
Question 34.Write a short note on electric bell.
Answer:A bell work on the principle of electromagnet. That is conversion of a conductor wire into magnet when electricity is passed through it. All bell whether they are advance or old they have this common principle.
Bell consist of following parts:
•Electromagnet
•Soft iron strip(hammer)
•Contact Screw
•Bell(metallic gong)
Working of bell:
•In its rest position the hammer is held away from the bell by its springy arm. When an electric current is enabled to pass through the winding of the electromagnet by closing of the switch.
•It creates a magnetic field from electromagnet that attracts the iron arm of the hammer, pulling it over to give the bell a tap. (Iron arm is just in front of the electromagnet in the picture)
•But this opens the circuit from the contact screw attached to the hammer arm, interrupting the current to the electromagnet.
•Thus, the magnetic field of the electromagnet collapses, and the hammer springs away from the bell.
•This closes the circuit again from contact screw, allowing the current to flow to the electromagnet again, so again the magnet pulls the hammer over to strike the bell.
•This cycle repeats rapidly, many times per second, resulting in a continuous ringing.
Question 35.Describe domestic electric circuit with the help of a diagram.
Answer:A common house has a very simple electric system. Which consist of three types of wire:
•Earthing (Green wire)
•Live (Red wire)
•Neutral (Black Wire)
Electricity is generated in power stations from there it reaches our houses from very thick wires over electric poles. And then it reaches in every corner of our house. The circuit which show how it reaches in every corner is shown in the picture:
Live wire and neutral wire: As the name suggest these are the main wires that is, they are the positive terminal and negative terminal of the circuit (respectively). The potential difference between these two wires is 220 V and the frequency of the alternating current provided by these wires is 50 Hertz.
These wires from electric boards fuse passes through the electricity meter of the house, then they are connected to the main switch of the house. From there all the appliances are connected in parallel to the main switch. The reason behind parallel connection is to provide same voltage to each plug/device.
Earthing Wire: It is the safety measure to prevent shocks and device damage. Devices like electric motor, heater, iron and refrigerator use very high amount of current.
So sometimes, there is a leak of electricity/current from these devices, this may cause very harmful damage to anyone.
So, to prevent such type of situation there is earthing wire, which basically absorb all the leaked current from the device and dump it to the earth. As, earthing wire is connected between metallic plates of device and earth. Earth then absorb all the leaked current and prevent us from any danger.
Question 36.Describe the principle, construction and working of an electric motor along with a figure.
Answer:v PRINCIPLE: An Electric motor works on the principle of conversion of electrical energy into mechanical energy. The main point here to note and keep in mind is that current has its own magnetic field.
v Construction of a sample small electric motor:
•A loop SNMT of an insulated copper wire is placed in a permanent magnetic field such that part ST and NM of the wire is perpendicular to the applied magnetic field.
•The ends of this wire are connected to two semicircular rings A and B which are adjusted on an axle for their easy rotation.
•The outer part of the rings are connected to batteries by stationary brushes.
v Working of a electric motor:-
When current is provided to the electric motor, the wire SNMT inside the motor get magnetised due to flow of current.
But the part SN and TM are parallel to the applied magnetic field so there will be no force acting on them, but the part ST and NM is perpendicular to the magnetic field hence a magnetic force acts on them and the part ST move upward. Now, the part SN is perpendicular to the magnetic field, so it move downward. Which complete one rotation of the wire SNMT. This goes on till there is current in the magnetic field.
The direction of movement is determined by Fleming's left-hand rule.
Question 37.Describe the principle, construction and working of an electric generator with a figure.
Answer:v Principle
Electric generator is a device which works on the principle of Electromagnetic Induction. The main point here to note and keep in mind is that a changing magnetic field can induce current in a conductor.
v Construction of a simple generator
•A loop ABCD of an insulated copper wire is placed in a permanent magnetic field such that part BC and AD of the wire is perpendicular to the applied magnetic field.
•The ends of this wire are connected to two semicircular full rings R1 and R2 which are adjusted on an axle for their easy rotation.
•The outer part of the rings are connected to Galvanometer by stationary brushes B1 and B2.
The construction of the motor and generator is same, just batteries in motor are replaced by galvanometer to detect current.
Here R1 and R2 two full rings and B1 and B2 are brushes.
v Working of the generator
•Inside the generator there is a conductor wire ABCD placed between fixed strong magnets.
•A mechanical rotation is provided to the loop wire ABCD.
•The wire is already placed in strong magnetic field of a strong magnet.
•So, the motion of the wire changes the magnetic field associated with the conductor loop ABCD and induce an electric current in the wire.
•One important point to notice is that generator provides an alternating current because which can be explained as follow: As the part AB go up CD come down, which induce the current in one direction. But as the AB part come down CD part go up, which induces the current in opposite direction. If the wire ABCD is connected to full rings it will produce Alternating current but if they are connected to half rings they will generate only Direct Current.
•That is how alternating current/Direct current is produced from a generator. The direction of induced current is determined by Fleming's right-hand rule.
The direction of magnetic field lines in a region outside the bar magnet is ______
A. From the N pole towards the S pole of a magnet.
B. From the S pole towards the N pole of a magnet.
C. In the direction coming out from both the poles of a magnet.
D. In the direction entering in both the poles of a magnet.
Answer:
As we know magnetic field lines always form closed loop. Inside the magnet the direction of magnetic field lines is from South Pole of the magnet to the North Pole of the magnet. But when the magnetic field lines come out of the North Pole, they have to form a closed loop, so they turn in outside region to go back to the South Pole. Hence, that is why direction of magnetic field lines in a region outside the bar magnet from the N pole towards the S pole of a magnet.
Question 2.
Which of the following statements is false?
A. The direction of magnetic field lines is from N to S.
B. In the region where the magnetic field lines are at a close distance from each other, there will be a strong magnetic field.
C. The magnetic field lines form closed loops.
D. The magnetic field lines can cross each other.
Answer:
According to statement A, the direction of the magnetic field line is from N to S, which is true.
According to statement B closer the magnetic field lines stronger the magnetic field there. We can think it like magnetic field lines are very close to each other near the magnetic bar. But as we go far away they also start separating and show weak magnetic field.
According to statement C magnetic field lines always form close loop. They can never have loose ends. They always start from a pole and end up on the other pole.
But according to statement D magnetic field lines can cross each other, which is wrong. Magnetic field lines always form close loop. And at any point, magnetic field always have a certain direction but if magnetic field lines cross each other, that will result into two directions of a magnetic field on a single point which is impossible.
Question 3.
By which instrument the presence of a magnetic field can be determined?
A. Voltmeter
B. Ammeter
C. Galvanometer
D. Magnetic needle.
Answer:
Voltmeter is a device which is used to measure the voltage in a circuit.
Similarly, Ammeter and Galvanometer are devices which are used to measure the current in a circuit.
But the Magnetic needle is an object which has its own natural magnetism. We do not have to connect it any circuit to start its magnetic properties. The presence of that magnetism will disturb the magnetic field present and there will be a force on the magnetic needle which will cause its movement. And that is how magnetic needle detects the presence of magnetic field.
Question 4.
Who had first observed the magnetic effect of an electric current?
A. Faraday
B. Oersted
C. Volta
D. Ampere.
Answer:
Oersted was a Danish physicist and chemist who discovered that electric currents create magnetic fields, which was the first connection found between electricity and magnetism. He noticed it when a compass needle is deflected when an electric current from a battery was switched on and off, confirming a direct relationship between electricity and magnetism.
While Faraday gives the concept of induction, Volta invented the battery and Ampere found about the current.
Question 5.
With the help of which law the direction of a magnetic field can be decided?
A. Faraday’s law
B. Fleming’s right-hand rule
C. Right-hand thumb rule
D. Fleming’s left-hand rule
Answer:
According to Right-hand thumb rule when we arrange our right-hand thumb in the direction of the current and as we wrap our finger around the current carrying conductor, the wrapped finger will show the direction of the magnetic current. This law helps in finding the direction of the magnetic field from a current carrying conductor. This law also implies that magnetic field and current will always be perpendicular.
While Fleming’s right-hand rule helps to find out the direction of the induced magnetic current. And Fleming’s left-hand rule helps to find out the direction of the magnetic force.
Question 6.
According to right-hand thumb rule, whose direction is indicated by a thumb?
A. Electric current
B. Magnetic field
C. Magnetic force
D. Motion of a conductor
Answer:
According to Right-hand thumb rule when we arrange our right hand's thumb in the direction of the current and as we wrap our finger around the current carrying conductor, the wrapped finger will show the direction of the magnetic field.
Hence, the thumb denotes the direction of current.
Question 7.
The magnetic field produced in a straight wire on passing the current through it is ______
A. in the direction of current
B. in the direction opposite to the current.
C. circular around the wire
D. in the direction parallel to the wire.
Answer:
The direction of the induced magnetic field from a current carrying conductor is given by the Right-hand thumb rule. According to Right-hand thumb rule when we arrange our right hand's thumb in the direction of the current and as we wrap our finger around the current carrying conductor, the wrapped finger will show the direction of the magnetic field.
So, that will result into a Circular ring around the wire.
Question 8.
What is the field line of a magnetic field passing through the centre of current carrying circular ring?
A. Circular
B. Straight line
C. Ellipse
D. The magnetic field is zero at the centre.
Answer:
The direction of the induced magnetic field from a current carrying conductor is given by The Right-hand thumb rule. In a case of a current carrying circular ring, we first divide the ring into various small parts and then we will see the contribution of each part.
First, consider the leftmost part which has a magnetic field which is coming out of the paper i.e. perpendicular to the paper. Similarly, when we consider the rightmost part whose magnetic field is also coming out of the paper and also perpendicular to the paper. So, while coming from left to right all the parts will contribute their magnetic fields similarly. And the resultant magnetic field at the center of the ring is coming out of the paper and perpendicular to the paper.
(In the figure we have to consider wire lying on a paper)
Now it is obvious that the ring lines are circular near the wire but when we come away from the wire they change and they approximately result into straight lines near the center of the ring because as distance increase the radius of the magnetic circle increase. Which is shown in the picture below:-
That is why the magnetic field lines are straight near the center of the current carrying circular ring.
Question 9.
Whose magnetic field is like a magnetic field of a bar magnet?
A. Current carrying wire
B. Current carrying ring.
C. Current carrying solenoid
D. Current carrying rectangular loop
Answer:
The magnetic field of a bar magnet is shown in the first figure. In which we can see inside the magnet the direction of the magnetic field is from the South Pole to the North Pole. But outside the magnet it is from North to the South Pole, it is because magnetic field always forms close loop.
A solenoid is a device which is formed when an insulated current-carrying wire is bent into a coil with N number of loops or turns. It is like the wrapping of a wire on a cylindrical object. The individual magnetic field of each turn contribute and it results in a magnetic field which is like the magnetic field of a bar magnet. The direction of the magnetic field inside the solenoid is determined by Right-hand thumb rule. That is, the magnetic field inside the solenoid is directed from south to north but outside the solenoid, it is from North to South, which are a similar magnetic field like a bar magnet.
Question 10.
Who gave the principle of electromagnetic induction?
A. Faraday
B. Oersted
C. Ampere
D. Volta
Answer:
Michael Faraday was a scientist who contributed to the study of electromagnetism. His main discoveries include the underlying electromagnetic induction, diamagnetism, and electrolysis. His breakthrough came when he wrapped two insulated coils of wire around an iron ring and found that upon passing a current through one coil a momentary current was induced in the other coil. This phenomenon is now known as induction. In subsequent experiments, he found that if he moved a magnet through a loop of wire an electric current flowed in that wire. The current also flowed if the loop was moved over a stationary magnet.
Question 11.
Which is the direction of the magnetic force acting on a current carrying wire placed in a magnetic field?
A. along magnetic field
B. along the electric current
C. perpendicular to the magnetic field
D. opposite to magnetic field.
Answer:
The direction of the magnetic force acting on a current wire placed in a magnetic field is given by Fleming’s left hands rule.
According to Fleming’s Left-hand rule: - If we arrange our left hand's thumb, index finger and middle finger mutually perpendicular to each other. And if we put our index finger in the direction of magnetic field applied and center finger in direction of electric current then the thumb will point in the direction of the magnetic force.
So, as mentioned magnetic force, magnetic field and electric current all are perpendicular to each other.
Question 12.
How is a current carrying wire placed in a magnetic field so that magnetic field does not act on it?
A. Parallel to magnetic field
B. Perpendicular to magnetic field.
C. At an angle 40o with the magnetic field
D. Can be arranged anyway.
Answer:
When the current carrying wire is placed parallel or anti-parallel to the magnetic field then and only then the magnetic field does not act on it.
The magnetic force depends on four things:
•Amount of current
•The strength of Magnetic field
•Length of the wire which remain in the magnetic field
•And the angle between the current carrying conductor and magnetic field.
The most important criteria here is the angle between the current carrying conductor and the magnetic field. If the angle is 0° or 180° then there will be no force acting on the wire. But if the angle is 90° the force will be maximum. If you observe the pattern it goes on like that, at 0° the force is 0 but as the angle increases the force increases and at 90° the force reaches its maximum value. And then again it starts decreasing and it becomes 0 at 180°.
Question 13.
From which of the following cases, the induced current in the loop will not be obtained?
A. The loop is moved in the direction of the magnet.
B. The magnet is moved in the direction of the loop.
C. The loop and magnet are moved in the opposite directions with the same speed.
D. The loop and magnet are moved in one direction with the same speed.
Answer:
The current will only induce in the coil if the magnetic field around the coil changes. This can only happen when:
•Magnet move towards the coil or move away from it.
•Coil move toward the magnet or move away from it.
•Both move towards each other {or we can also say loop and magnet move in opposite direction with same speed.}
These five condition are the only condition for induction of current in the loop.
But, in option D the magnet and loop are moving in one direction let's say positive X-axis with same speed. Such movement will not change the magnetic field between them because the distance between them is also constant.
So, option A, B, C will result into induction of current but option D won't.
Question 14.
Which instrument is used in converting electrical energy into mechanical energy?
A. Electric generator
B. Electric motor
C. Electric iron
D. Electric oven
Answer:
An Electric motor converts electrical energy into mechanical energy. The main point here to note is that a current has its magnetic field. Working:-
•Inside the motor there is a conductor wire placed between fixed strong magnets.
•When current is provided to the electric motor the wire inside the motor get magnetised due to flow of current.
•These wires are already placed in strong magnetic field of a strong magnet.
•This cause a repulsion between the wire and the strong magnets. This repulsion cause movement of wire. The direction of movement is determined by Fleming's left hand rule.
Electric motor is use for doing very mechanical works. It has a very widespread application like in fan, car, etc.
Question 15.
On which principle does the electric generator work?
A. Electrical energy is converted into mechanical energy.
B. Electrical energy is converted into thermal energy.
C. Mechanical energy is converted into electrical energy.
D. Electrical energy is converted into light energy.
Answer:
Electric generator is a device which converts mechanical work into electrical energy. The main point here to note is that a changing magnetic field can induce current in a conductor. Working of the generator:
•Inside the generator there is a conductor wire placed between fixed strong magnets.
•When mechanical rotation is provided to that wire the magnetic field associated with the wire changes.
•Those wire are already placed in strong magnetic field of a strong magnet.
•So, the motion of the wire changes the magnetic field and induce an electric current in the wire.
•The direction of induced current is determined by Fleming's right hand rule.
Question 16.
The magnitude of an AC voltage used in India is _________ and the frequency is _____.
A. 110 V, 60Hz
B. 110V, 50Hz
C. 220V, 50Hz
D. 220V, 60HZ
Answer:
Frequency of an AC current implies number of complete wave present in a second. 50 hertz frequency means that there are 50 waves present in an interval of one second.
Most of the houses in India are provided with 220 V voltage and it is further modified according to the voltage requirement of the devices.
Question 17.
Which coloured wire is used for earthing?
A. Red
B. Black
C. Green
D. Can be of any colour.
Answer:
Basically earthing wire is the safety measure to prevent shocks and device damages. Devices like electric motor, heater, iron and refrigerator use very high amount of current. Whenever there is a leak of electricity/current from these devices, the leaked current reaches the metallic plates of these devices and if we touch them with bare hand we will get a shock. This may cause very harmful damage.
So, to prevent such type of situation there is earthing wire, which basically absorb all the leaked current from the device and dump it to the earth. This dumping of leaked current from the device is very useful as it prevents damage to the device as well as human.
Question 18.
Which type of current is obtained from a battery?
A. DC current
B. AC current
C. Voltmeter
D. Magnetic needle
Answer:
A battery is a source to Direct Current (DC). It provide a constant value of current which does not change with the time. This is because in a battery there are two terminal one positive and one negative and the current flows only from positive terminal to the negative terminal. It flows in one direction only that is from positive to negative which is the characteristic of DC current. Hence, that is why battery is source of DC current.
If the current varies its value that is positive to negative and negative to positive then the current is said to be Alternating Current (AC).
Question 19.
Which instrument is used to know the presence of an electric current?
A. Fuse
B. Galvanometer
C. Voltmeter
D. Magnetic needle
Answer:
Galvanometer is a very sensitive device which measures the amount of current as well as the direction of current. From the Induction of Current experiment we see that the induced current changes its direction when we move magnet towards the coil and when we move away from it. It is a sensitive device so it is mainly use to find out the presence of current rather than the amount of current.
While Voltmeter is used to measure voltage, magnetic needle is used to find out the presence of magnetic field and fuse is for safety purposes in an electric circuit.
Question 20.
A fuse wire is _______________
A. conductor
B. insulator
C. semiconductor
D. made up of any material
Answer:
A fuse wire is basically a safety measure to prevent electric fires and short circuits. Fuse wire is a conductor wire with a very low melting point. Low melting point is the main characteristic here.
•Some devices require very high amount of current, the flow of so much current can sometime cause the melting of the insulating wire due to heating effect of the electric current.
•This can result into severe electric fires. To prevent these situation a fuse is introduced into the circuit, which is made up of a low melting point conductor wire.
•The wire inside the conductor melts and breaks the circuit as soon as the heating due to current increases.
This prevents further fire or electric short circuit.
Question 21.
__________ rule is used to know the direction of an induced current in the circuit.
A. Fleming’s left hand
B. Fleming’s right hand
C. Right hand thumb
D. Ampere's
Answer:
As we know from Faraday's law that a current induces in a conductor whenever conductor is moving through a magnetic field.
Fleming' right hand rule is use to find out the direction of the induced current within a conductor, when the conductor is moving in a magnetic field.
•According to the Fleming’s right hand rule, if we put our thumb, index finger and middle finger mutually perpendicular to each other.
•Such that thumb points in the direction of the motion of conductor and index finger point in the direction of the applied magnetic field. The given picture illustrates the rule:
•Then middle/centre finger will show the direction of the induced or generated current within the conductor.
Question 22.
How many times does an AC electric current with the frequency 50Hz change its direction?
A. 25
B. 50
C. 100
D. 200
Answer:
To answer the question we have to first understand it. Frequency of an AC current implies number of complete wave present in a second. 50 hertz frequency means that there are 50 waves present in an interval of one second. The given picture will clear all he doubt,
In the picture there is only one complete wave in a second, hence its frequency is 1 hertz. Also observe that in one wave the current change its direction twice first positive than negative.
Now, if the frequency of the current is 50 hertz, which means that there are 50 such waves present in one second and then the current will change its direction 100 times.
Question 23.
At the centre of which of the following four circular rings has maximum magnetic field while passing equal current through each one?
A.
B.
C.
D.
Answer:
The direction of the induced magnetic field from a current carrying conductor is given by the Right hand thumb rule. In a case of a current carrying circular ring, magnetic field at the centre of the ring is coming out of the paper and perpendicular to the paper.
Now it is obvious that the magnetic field is stronger near the wire but when we come away from the wire it weakens and at the centre of the ring it is weakest. Hence, more the radius the ring the more magnetic field is weak at centre of the ring.
So, (d) will have the weakest magnetic field at centre and (a) has the strongest magnetic field at centre.
Question 24.
Give the characteristic of magnetic field lines.
Answer:
Following are some characteristics of the magnetic field lines:
•The direction of magnetic field inside the magnet is from S to N. Which we have observed, but outside the magnet the direction of magnetic field lines is from North to South, the reason behind that is the next characteristic.
•Magnetic field lines always form close loop. They can never have loose ends. They always start from a pole and end up on another pole. This characteristic is the most important characteristic this is also the reason behind why outside the magnet the direction of field line is north to south.
•Closure the magnetic field lines stronger the magnetic field there is. We can think it like magnetic field lines are very close to each other near the magnetic bar. But as we go far away they also start separating and show weak magnetic field.
•Magnetic field lines can never cross each other. Magnetic field lines always form close loop. And any point in a magnetic field always a certain direction but if magnetic field lines cross each other, that will result into two direction of a magnetic field on a single point which is impossible.
Question 25.
Explain the ‘right hand thumb rule’ to know the direction of magnetic field.
Answer:
The direction of the induced magnetic field from a current carrying conductor is given by the Right hand thumb rule. According to Right hand thumb rule:-
•When we place our right hand's thumb in the direction of the current and as we wrap our finger around the current carrying conductor.
•Wrapped finger will show the direction of the magnetic field.
•It is noticeable that the wrapped finger from a close loop which is the most important property of the magnetic field.
Hence, when we place our right hand's thumb in the direction of the current carrying wire the circular rings formed by our finger will denote the magnetic field.
Question 26.
What will happen while placing a current conductor in a magnetic field? Explain.
Answer:
Whenever a current carrying conductor is placed in a magnetic field then the conductor will experience a magnetic force. This happen because the current in the conductor has its own magnetic field and there is also a magnetic field present. So both the field will interact and will result in repulsion or attraction of the conductor wire toward the fixed magnets.
The magnetic force depend on four things:
•Amount of current
•Strength of Magnetic field
•Length of the wire which remain in magnetic field
•And the angle between the current carrying conductor and magnetic field.
The direction of magnetic force acting on a current wire placed in a magnetic field is given by Fleming’s left hands rule.
Question 27.
By which law can the direction of an induced electric current can be determined? Give the explanation of the law.
Answer:
Fleming' right hand rule is use to find out the direction of the induced current within a conductor. As we know from Faraday's law that a current induces in a conductor whenever conductor is moving through a magnetic field.
So, according to the Fleming’s right hand rule,
•If we put our thumb, index finger and middle finger mutually perpendicular to each other. As shown in the picture.
•Such that thumb points in the direction of the motion of conductor and index finger point in the direction of the applied magnetic field.
•Then middle/centre finger will show the direction of the induced or generated current within the conductor.
Question 28.
Explain the provision of the earthing wire.
Answer:
Basically earthing wire is the safety measure to prevent shocks and device damage. The following points will clarify:
•Devices like electric motor, heater, iron and refrigerator use very high amount of current.
•So sometimes, there is a leak of electricity/current from these devices, the leaked current reaches the metallic plates present under these devices and if we touch such devices with bare hand we will get a shock. This may cause very harmful damage.
•So, to prevent such type of situation there is earthing wire, which basically absorb all the leaked current from the device and dump it to the earth. As, earthing wire is connected between metallic plates of device and earth. Earth then absorb all the leaked current and prevent us from any danger.
This dumping of leaked current from the device is very useful as it prevents damage to the device as well as human.
Question 29.
Mention the usefulness of a fuse in a domestic electrical circuit.
Answer:
A fuse wire is a safety measure to prevent electric fires and short circuits. Some usefulness of Fuse:
•Without using Fuse we will be facing daily short circuited electric circuits.
•Device which require high current can damage permanently causing loss of money and resources.
•Also, fuse prevents electric fires.
Basically, Fuse wire is a conductor wire with a very low melting point. Low melting point is the main characteristic here. Working of fuse wire:
•Some devices require very high amount of current, the flow of so much current can sometime cause the melting of the insulating wire due to heating effect of the electric current.
•This can result into severe electric fires. To prevent these situation a fuse is introduced into the circuit, which is made up of a low melting point conductor wire.
•The wire inside the conductor melts and breaks the circuit as soon as the heating due to current increases.
This prevents further fire or electric short circuit.
Question 30.
Discuss the magnetic field resulting from a current carrying circular ring.
Answer:
In a case of a current carrying circular ring, we first divide the ring into various small parts and then we will see contribution of each part.
•First consider the leftmost part which have a magnetic field which is coming out of the paper i.e. perpendicular to the paper.
•Similarly, when we consider the rightmost part whose magnetic field is also coming out of the paper and also perpendicular to the paper.
•So, while coming from left to right all the parts will contribute their magnetic fields similarly. And the resultant magnetic field at the centre of the ring is coming out of the paper and perpendicular to the paper.
(The resultant magnetic field of the ring.)
Now it is obvious that the ring lines are circular near the wire but when we come away from the wire they change and they nearly convert into straight lines near the centre of the ring because the radius of the magnetic circle increase as we move towards the centre of the ring which result into the straight light of magnetic field lines.
Question 31.
What is solenoid? Give the characteristics of magnet from solenoid.
Answer:
A solenoid is a device which is formed when an insulated current carrying wire is bent into a coil with an N number of loops or turns. It is like wrapping of a wire on a cylindrical object.
•The individual magnetic field of each turn contribute and it results into a magnetic field which is like the magnetic field of a bar magnet.
•The magnetic field of the solenoid depend on the number of turns present. It is directly proportional to the number of turns, ore number of turns more strong magnetism. For example if we have to lift a very have metal pipe we would use a solenoid with very large number of turns, as they will have a stronger magnetic field. In simple terms the magnetism of a solenoid is controllable.
•Furthermore the magnetism of a solenoid can be increased by putting an iron rod through the coils.
•The direction of that magnetic field inside the solenoid is determined by Right hand thumb rule which is directed from south to north but outside the solenoid it is from North to South.
Question 32.
What precautions should be taken during the use of electricity?
Answer:
Electricity is as dangerous as it is useful, in dealing with electricity or electric device one must be very careful. Carelessness may even cause death. There is no escape from it. We use electricity in our household and daily life, here are some precautions we should do to prevent any kind of loss:
1. Always use appropriate insulated rubber gloves and goggles while working on any branch circuit or any other electrical circuit.
2. Avoid water at all times when working with electricity. Never touch or try repairing any electrical equipment or circuits with wet hands.
3. Never use any electrical device with broken cords, damaged insulation or broken plugs.
4. Do not touch anything without complete knowledge. This may cause severe damage.
5. Follow the safety rules established by the companies of the device which you are handling.
6. Never use an aluminium or steel ladder if you are working on any receptacle at height in your home. Use a bamboo, wooden or a fibreglass ladder instead.
7. Always wear rubber slippers/shoes while handling electricity.
Question 33.
Describe the experiment that explains the phenomenon of an electromagnetic induction and give its conclusion.
Answer:
The experiment was first done by Michael Faraday. He observed that the current will only induce in the coil if the magnetic field around the coil changes.
In the experiment, he first made a loop of conducting wire and connect a galvanometer with it to record the observation. Then he performed the following things and recorded observation in each case:
•He move a magnet towards the coil or move away from it.
•He made an observation also when both are stationary.
•Then he moved the Coil toward the magnet or move away from it.
•Then he move both of them towards each other.
Result of the experiment: From the observation he concluded that whenever the magnetic field around a conductor wire changes it produces current in the wire. His first, second and third observation resulted in a deflection produced in the galvanometer because as the coil or magnet moves the magnetic field changes. But in the second observation both of them were steady which results in no induction current.
Conclusion of the experiment: He finally concluded that whenever magnetic field around a conductor wire changes, results in induction of the current.
Question 34.
Write a short note on electric bell.
Answer:
A bell work on the principle of electromagnet. That is conversion of a conductor wire into magnet when electricity is passed through it. All bell whether they are advance or old they have this common principle.
Bell consist of following parts:
•Electromagnet
•Soft iron strip(hammer)
•Contact Screw
•Bell(metallic gong)
Working of bell:
•In its rest position the hammer is held away from the bell by its springy arm. When an electric current is enabled to pass through the winding of the electromagnet by closing of the switch.
•It creates a magnetic field from electromagnet that attracts the iron arm of the hammer, pulling it over to give the bell a tap. (Iron arm is just in front of the electromagnet in the picture)
•But this opens the circuit from the contact screw attached to the hammer arm, interrupting the current to the electromagnet.
•Thus, the magnetic field of the electromagnet collapses, and the hammer springs away from the bell.
•This closes the circuit again from contact screw, allowing the current to flow to the electromagnet again, so again the magnet pulls the hammer over to strike the bell.
•This cycle repeats rapidly, many times per second, resulting in a continuous ringing.
Question 35.
Describe domestic electric circuit with the help of a diagram.
Answer:
A common house has a very simple electric system. Which consist of three types of wire:
•Earthing (Green wire)
•Live (Red wire)
•Neutral (Black Wire)
Electricity is generated in power stations from there it reaches our houses from very thick wires over electric poles. And then it reaches in every corner of our house. The circuit which show how it reaches in every corner is shown in the picture:
Live wire and neutral wire: As the name suggest these are the main wires that is, they are the positive terminal and negative terminal of the circuit (respectively). The potential difference between these two wires is 220 V and the frequency of the alternating current provided by these wires is 50 Hertz.
These wires from electric boards fuse passes through the electricity meter of the house, then they are connected to the main switch of the house. From there all the appliances are connected in parallel to the main switch. The reason behind parallel connection is to provide same voltage to each plug/device.
Earthing Wire: It is the safety measure to prevent shocks and device damage. Devices like electric motor, heater, iron and refrigerator use very high amount of current.
So sometimes, there is a leak of electricity/current from these devices, this may cause very harmful damage to anyone.
So, to prevent such type of situation there is earthing wire, which basically absorb all the leaked current from the device and dump it to the earth. As, earthing wire is connected between metallic plates of device and earth. Earth then absorb all the leaked current and prevent us from any danger.
Question 36.
Describe the principle, construction and working of an electric motor along with a figure.
Answer:
v PRINCIPLE: An Electric motor works on the principle of conversion of electrical energy into mechanical energy. The main point here to note and keep in mind is that current has its own magnetic field.
v Construction of a sample small electric motor:
•A loop SNMT of an insulated copper wire is placed in a permanent magnetic field such that part ST and NM of the wire is perpendicular to the applied magnetic field.
•The ends of this wire are connected to two semicircular rings A and B which are adjusted on an axle for their easy rotation.
•The outer part of the rings are connected to batteries by stationary brushes.
v Working of a electric motor:-
When current is provided to the electric motor, the wire SNMT inside the motor get magnetised due to flow of current.
But the part SN and TM are parallel to the applied magnetic field so there will be no force acting on them, but the part ST and NM is perpendicular to the magnetic field hence a magnetic force acts on them and the part ST move upward. Now, the part SN is perpendicular to the magnetic field, so it move downward. Which complete one rotation of the wire SNMT. This goes on till there is current in the magnetic field.
The direction of movement is determined by Fleming's left-hand rule.
Question 37.
Describe the principle, construction and working of an electric generator with a figure.
Answer:
v Principle
Electric generator is a device which works on the principle of Electromagnetic Induction. The main point here to note and keep in mind is that a changing magnetic field can induce current in a conductor.
v Construction of a simple generator
•A loop ABCD of an insulated copper wire is placed in a permanent magnetic field such that part BC and AD of the wire is perpendicular to the applied magnetic field.
•The ends of this wire are connected to two semicircular full rings R1 and R2 which are adjusted on an axle for their easy rotation.
•The outer part of the rings are connected to Galvanometer by stationary brushes B1 and B2.
The construction of the motor and generator is same, just batteries in motor are replaced by galvanometer to detect current.
Here R1 and R2 two full rings and B1 and B2 are brushes.
v Working of the generator
•Inside the generator there is a conductor wire ABCD placed between fixed strong magnets.
•A mechanical rotation is provided to the loop wire ABCD.
•The wire is already placed in strong magnetic field of a strong magnet.
•So, the motion of the wire changes the magnetic field associated with the conductor loop ABCD and induce an electric current in the wire.
•One important point to notice is that generator provides an alternating current because which can be explained as follow: As the part AB go up CD come down, which induce the current in one direction. But as the AB part come down CD part go up, which induces the current in opposite direction. If the wire ABCD is connected to full rings it will produce Alternating current but if they are connected to half rings they will generate only Direct Current.
•That is how alternating current/Direct current is produced from a generator. The direction of induced current is determined by Fleming's right-hand rule.