Goyal Brothers Textbook Solutions: Electromagnetism

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Electromagnetism 
 
Exercise – 1 
Question 1. 
When can an electric charge give rise to a magnetic field? 
Answer: 
When electric charge is in motion e. charge flows, it gives rise to magnetic field. 
Question 2. 
Describe Oersted’s experiment to show that a conductor carrying current produces a 
magnetic field around it 
Answer: 
Oersted’s Experiment : 
Set up the apparatus as shown in fig. when switch is in open circuit 
 
 
magnetic needle points in north direction. Showing there is no magnetic field around it. 
Now when switch is closed and current flows through the wire, the magnetic needle 
gets deflected from north. This shows that conductor carrying current produces 
magnetic field around it and deflects the magnetic needle. 
Question 3. 
(a) How will you plot the magnetic field lines around a straight conductor carrying 
current ? 
(b) State two rules by which you can determine the direction of the magnetic field 
around a straight conductor. 
Answer: 
(a) To plot the magnetic field lines around a straight conductor carrying current: Pass 
straight conductor through a cardboard or glass-plate. And pass current. 
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Electromagnetism 
 
Exercise – 1 
Question 1. 
When can an electric charge give rise to a magnetic field? 
Answer: 
When electric charge is in motion e. charge flows, it gives rise to magnetic field. 
Question 2. 
Describe Oersted’s experiment to show that a conductor carrying current produces a 
magnetic field around it 
Answer: 
Oersted’s Experiment : 
Set up the apparatus as shown in fig. when switch is in open circuit 
 
 
magnetic needle points in north direction. Showing there is no magnetic field around it. 
Now when switch is closed and current flows through the wire, the magnetic needle 
gets deflected from north. This shows that conductor carrying current produces 
magnetic field around it and deflects the magnetic needle. 
Question 3. 
(a) How will you plot the magnetic field lines around a straight conductor carrying 
current ? 
(b) State two rules by which you can determine the direction of the magnetic field 
around a straight conductor. 
Answer: 
(a) To plot the magnetic field lines around a straight conductor carrying current: Pass 
straight conductor through a cardboard or glass-plate. And pass current. 
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From A to B direction in the upward direction. Sprinkle iron filings on glass plate. Tap 
the glass plate, the iron filing will arrange themselves in circles around the conductor 
along the magnetic lines of force. The magnetic fields are circular in nature. The 
direction of magnetic field can be detected with the help of magnetic compass and 
direction is found anti clock wise. 
(b) Two rules are : 
1. Right hand thumb rule: “Imagine you are holding the current carrying wire in your 
right-hand so that your thumb points in the direction of current, then the direction 
in which your fingers encircle the wire will give the direction of magnetic field lines 
around the wire.” 
 
2. Max Well’s Screw Rule : “Imagine driving a cork screw in the direction of current, 
then the direction in which we turn its handle is the direction of magnetic field (or 
magnetic field lines). 
 
Question 4. 
(a) Draw a set up for plotting magnetic field around a circular coil carrying current. 
(b) State the properties of the magnetic field in 4(a). 
Answer: 
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Electromagnetism 
 
Exercise – 1 
Question 1. 
When can an electric charge give rise to a magnetic field? 
Answer: 
When electric charge is in motion e. charge flows, it gives rise to magnetic field. 
Question 2. 
Describe Oersted’s experiment to show that a conductor carrying current produces a 
magnetic field around it 
Answer: 
Oersted’s Experiment : 
Set up the apparatus as shown in fig. when switch is in open circuit 
 
 
magnetic needle points in north direction. Showing there is no magnetic field around it. 
Now when switch is closed and current flows through the wire, the magnetic needle 
gets deflected from north. This shows that conductor carrying current produces 
magnetic field around it and deflects the magnetic needle. 
Question 3. 
(a) How will you plot the magnetic field lines around a straight conductor carrying 
current ? 
(b) State two rules by which you can determine the direction of the magnetic field 
around a straight conductor. 
Answer: 
(a) To plot the magnetic field lines around a straight conductor carrying current: Pass 
straight conductor through a cardboard or glass-plate. And pass current. 
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From A to B direction in the upward direction. Sprinkle iron filings on glass plate. Tap 
the glass plate, the iron filing will arrange themselves in circles around the conductor 
along the magnetic lines of force. The magnetic fields are circular in nature. The 
direction of magnetic field can be detected with the help of magnetic compass and 
direction is found anti clock wise. 
(b) Two rules are : 
1. Right hand thumb rule: “Imagine you are holding the current carrying wire in your 
right-hand so that your thumb points in the direction of current, then the direction 
in which your fingers encircle the wire will give the direction of magnetic field lines 
around the wire.” 
 
2. Max Well’s Screw Rule : “Imagine driving a cork screw in the direction of current, 
then the direction in which we turn its handle is the direction of magnetic field (or 
magnetic field lines). 
 
Question 4. 
(a) Draw a set up for plotting magnetic field around a circular coil carrying current. 
(b) State the properties of the magnetic field in 4(a). 
Answer: 
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(a) 
 
(b) Properties of the magnetic field : 
1. The magnetic field lines are circular near current carrying loop. 
2. At the center of the circular loop the magnetic field lines are in the same direction 
and strength of magnetic field increases. 
Question 5. 
What is a solenoid ? Draw a magnetic field around a solenoid, when direct current flows 
through it. How will you find the magnetic polarity of a solenoid without using a 
magnetic needle ? 
Answer: 
Solenoid : “Is a long coil containing a large number of close turns of insulated copper 
wire.” 
 
Magnetic polarity of solenoid can be determined like a bar magnet i.e. when it is 
suspended freely, it will come to rest pointing in North and South direction or polarity 
can be checked by bringing north pole of a bar magnet. The pole repelled by north pole 
must be North pole of solenoid. 
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Electromagnetism 
 
Exercise – 1 
Question 1. 
When can an electric charge give rise to a magnetic field? 
Answer: 
When electric charge is in motion e. charge flows, it gives rise to magnetic field. 
Question 2. 
Describe Oersted’s experiment to show that a conductor carrying current produces a 
magnetic field around it 
Answer: 
Oersted’s Experiment : 
Set up the apparatus as shown in fig. when switch is in open circuit 
 
 
magnetic needle points in north direction. Showing there is no magnetic field around it. 
Now when switch is closed and current flows through the wire, the magnetic needle 
gets deflected from north. This shows that conductor carrying current produces 
magnetic field around it and deflects the magnetic needle. 
Question 3. 
(a) How will you plot the magnetic field lines around a straight conductor carrying 
current ? 
(b) State two rules by which you can determine the direction of the magnetic field 
around a straight conductor. 
Answer: 
(a) To plot the magnetic field lines around a straight conductor carrying current: Pass 
straight conductor through a cardboard or glass-plate. And pass current. 
Downloaded from https://www.ncertbooksolutions.com/
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From A to B direction in the upward direction. Sprinkle iron filings on glass plate. Tap 
the glass plate, the iron filing will arrange themselves in circles around the conductor 
along the magnetic lines of force. The magnetic fields are circular in nature. The 
direction of magnetic field can be detected with the help of magnetic compass and 
direction is found anti clock wise. 
(b) Two rules are : 
1. Right hand thumb rule: “Imagine you are holding the current carrying wire in your 
right-hand so that your thumb points in the direction of current, then the direction 
in which your fingers encircle the wire will give the direction of magnetic field lines 
around the wire.” 
 
2. Max Well’s Screw Rule : “Imagine driving a cork screw in the direction of current, 
then the direction in which we turn its handle is the direction of magnetic field (or 
magnetic field lines). 
 
Question 4. 
(a) Draw a set up for plotting magnetic field around a circular coil carrying current. 
(b) State the properties of the magnetic field in 4(a). 
Answer: 
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(a) 
 
(b) Properties of the magnetic field : 
1. The magnetic field lines are circular near current carrying loop. 
2. At the center of the circular loop the magnetic field lines are in the same direction 
and strength of magnetic field increases. 
Question 5. 
What is a solenoid ? Draw a magnetic field around a solenoid, when direct current flows 
through it. How will you find the magnetic polarity of a solenoid without using a 
magnetic needle ? 
Answer: 
Solenoid : “Is a long coil containing a large number of close turns of insulated copper 
wire.” 
 
Magnetic polarity of solenoid can be determined like a bar magnet i.e. when it is 
suspended freely, it will come to rest pointing in North and South direction or polarity 
can be checked by bringing north pole of a bar magnet. The pole repelled by north pole 
must be North pole of solenoid. 
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Question 6. 
How does the magnetic field set up in a solenoid changes when: 
(a) number of turns are increased ? 
(b) diameter of the solenoid is increased ? 
(c) strength of the current is increased ? 
(d) a soft iron core is placed in it ? 
Answer: 
(a) When number of turns are increased magnetic field will be stronger. 
(b) When diameter of the solenoid is increased but diameter should be less than the 
length of solenoid, so that parallel lines should add up to give a stronger field. 
(c) When strength of current is increased stronger will be the magnetic field produced. 
(d) When soft iron core is placed in the solenoid very strong magnetic field is produces. 
Question 7. 
Give four differences between an electromagnet and a permanent magnet. 
Answer: 
Differences between electromagnet and permanent magnet: 
Electromagnet: 
1. It is temporary magnet 
2. It strength can be changed, by changing the current. 
3. Polarity can be changed by changing the direction of current. 
4. Produces very strong magnetic force. 
Permanent Magnet 
1. It is permanent magnet. 
2. It strength cannot be changed. 
3. Polarity cannot be changed. 
4. Produces weak magnetic force. 
Question 8. 
State four practical applications of electromagnets. 
Answer: 
Four applications of electromagnet : 
1. In electric bell. 
2. In magnetising steel bars. 
3. For scanning machines (MRI) 
4. In electric motor, generator. 
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Electromagnetism 
 
Exercise – 1 
Question 1. 
When can an electric charge give rise to a magnetic field? 
Answer: 
When electric charge is in motion e. charge flows, it gives rise to magnetic field. 
Question 2. 
Describe Oersted’s experiment to show that a conductor carrying current produces a 
magnetic field around it 
Answer: 
Oersted’s Experiment : 
Set up the apparatus as shown in fig. when switch is in open circuit 
 
 
magnetic needle points in north direction. Showing there is no magnetic field around it. 
Now when switch is closed and current flows through the wire, the magnetic needle 
gets deflected from north. This shows that conductor carrying current produces 
magnetic field around it and deflects the magnetic needle. 
Question 3. 
(a) How will you plot the magnetic field lines around a straight conductor carrying 
current ? 
(b) State two rules by which you can determine the direction of the magnetic field 
around a straight conductor. 
Answer: 
(a) To plot the magnetic field lines around a straight conductor carrying current: Pass 
straight conductor through a cardboard or glass-plate. And pass current. 
Downloaded from https://www.ncertbooksolutions.com/
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https://www.ncertbooksolutions.com
 
From A to B direction in the upward direction. Sprinkle iron filings on glass plate. Tap 
the glass plate, the iron filing will arrange themselves in circles around the conductor 
along the magnetic lines of force. The magnetic fields are circular in nature. The 
direction of magnetic field can be detected with the help of magnetic compass and 
direction is found anti clock wise. 
(b) Two rules are : 
1. Right hand thumb rule: “Imagine you are holding the current carrying wire in your 
right-hand so that your thumb points in the direction of current, then the direction 
in which your fingers encircle the wire will give the direction of magnetic field lines 
around the wire.” 
 
2. Max Well’s Screw Rule : “Imagine driving a cork screw in the direction of current, 
then the direction in which we turn its handle is the direction of magnetic field (or 
magnetic field lines). 
 
Question 4. 
(a) Draw a set up for plotting magnetic field around a circular coil carrying current. 
(b) State the properties of the magnetic field in 4(a). 
Answer: 
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(a) 
 
(b) Properties of the magnetic field : 
1. The magnetic field lines are circular near current carrying loop. 
2. At the center of the circular loop the magnetic field lines are in the same direction 
and strength of magnetic field increases. 
Question 5. 
What is a solenoid ? Draw a magnetic field around a solenoid, when direct current flows 
through it. How will you find the magnetic polarity of a solenoid without using a 
magnetic needle ? 
Answer: 
Solenoid : “Is a long coil containing a large number of close turns of insulated copper 
wire.” 
 
Magnetic polarity of solenoid can be determined like a bar magnet i.e. when it is 
suspended freely, it will come to rest pointing in North and South direction or polarity 
can be checked by bringing north pole of a bar magnet. The pole repelled by north pole 
must be North pole of solenoid. 
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Question 6. 
How does the magnetic field set up in a solenoid changes when: 
(a) number of turns are increased ? 
(b) diameter of the solenoid is increased ? 
(c) strength of the current is increased ? 
(d) a soft iron core is placed in it ? 
Answer: 
(a) When number of turns are increased magnetic field will be stronger. 
(b) When diameter of the solenoid is increased but diameter should be less than the 
length of solenoid, so that parallel lines should add up to give a stronger field. 
(c) When strength of current is increased stronger will be the magnetic field produced. 
(d) When soft iron core is placed in the solenoid very strong magnetic field is produces. 
Question 7. 
Give four differences between an electromagnet and a permanent magnet. 
Answer: 
Differences between electromagnet and permanent magnet: 
Electromagnet: 
1. It is temporary magnet 
2. It strength can be changed, by changing the current. 
3. Polarity can be changed by changing the direction of current. 
4. Produces very strong magnetic force. 
Permanent Magnet 
1. It is permanent magnet. 
2. It strength cannot be changed. 
3. Polarity cannot be changed. 
4. Produces weak magnetic force. 
Question 8. 
State four practical applications of electromagnets. 
Answer: 
Four applications of electromagnet : 
1. In electric bell. 
2. In magnetising steel bars. 
3. For scanning machines (MRI) 
4. In electric motor, generator. 
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Question 9. 
(a) On what factors does the force experienced by a straight conductor placed in a 
magnetic field depend 
(b) State the law which determines the force experienced by a conductor. 
Answer: 
(a) Factors on which force experienced by a straight conductor depend : 
1. Current passing : direct proportional to current passing. 
2. Inversely proportional to the distance of that point from the wire. 
(b) When a conductor carrying current is placed in a magnetic field in a direction other 
them the direction of magnetic field, experiences a force called Lorentz force. This force 
is perpendicular to both, the direction of current I and the direction of magnetic fields B. 
This law is called : 
Fleming’s left hand rule : “Stretch the fore finger, control finger and the thumb of your 
left hand mutually perpendicular to each other. If the fore-finger points in the direction 
of magnetic field, central finger indicates the direction of current, then the thumb will 
indicate the direction of motion of conductor (i.e., force on conductor) 
Question 10. 
(a) Draw a neat and labelled diagram of a d.c. motor and explain its construction and 
working. 
(b) How can you make a d.c. motor more powerful ? 
(c) How can you convert its jerky motion into uniform circular motion ? 
Answer: 
(a) D.C. Motor 
 
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