415 + Interview Questions in ELECTROMAGNETISM IN GENERAL AWARENESS Page 3 InterviewSolution

101.	The radius of a circular ring of wire is R and it carries a current of I ampere. At its centre a smaller ring of radius r with current i and N turns is placed. Assuming that the planes of two rings are perpendicular to each other and the magnetic induction produced at the centre of bigger ring is constant, then the torque acting on smaller ring will be -A. `Nipir^(2) xx {(mu_(0)I)/(2R)}`B. zeroC. `Nir^(2) xx {(mu_(0)I)/(2R)}`D. `Nir^(2){(I^(2))/(2R)}`
Answer» Correct Answer - A

Discussion

102.	The effective radius of a circular coil is R and number of turns is N. The current through it is i ampere. The work done is rotating the coil from angle `theta = 0^(@)` to `theta = 180^(@)` in an external magnetic field B will be -A. `piNiR^(2)B`B. `2piNiR^(2)B`C. `(2NiB)//(piR^(2))`D. `4piNiR^(2)B`
Answer» Correct Answer - B

Discussion

103.	A current of 2 ampere is flowing through a coil of radius 0.1 m and having 10 turns. The magnetic moment of the coil will be :A. `20 A-m^(2)`B. `2A-m^(2)`C. `0.314 A-m^(2)`D. `0.628 A-m^(2)`
Answer» Correct Answer - D

Discussion

104.	An electric current of I ampere is flowing in a long conductor CG as shown in figure. Find the magnitude and direction of magnetic induction at the centre O of circular part. A. `(mu_(0)i)/(8r)`B. `(mu_(0)i)/(4r)`C. `(mu_(0)i)/(16r)`D. `0`
Answer» Correct Answer - C

Discussion

105.	An electric current of I ampere is flowing in a long conductor CG as shown in figure. Find the magnitude and direction of magnetic induction at the centre O of circular part. A. `(mu_(0)i)/(2r)(1+(1)/(mu)), o.`B. `0`C. `(mu_(0)i)/(2r)(1-(1)/(mu)), ox`D. `(mu_(0)i)/(2r),o.`
Answer» Correct Answer - A

Discussion

106.	The conductor ABCDE has the shape shown. It lies in the yz plane, with A and E on the y-axis. When it moves with a velocity v in a magnetic field B, an emf e is induced between A and E.(a) e = 0, if v is in the y-direction and B is in the x-direction. (b) e = 2Bav, if v is in the y-direction and B is in the x-direction. (c) e = Bλv, if v is in the z-direction and B is in the x-direction. (d) e = Bλv, if v is in the x-direction and B is in the z-direction.
Answer» Correct Answer is: (a, c, & d)

Discussion

107.	A flat coil of n turns, area A and carrying a current i is placed in a uniform magnetic field of magnitude B. The plane of the coil makes an angle θ with the direction of the field. The torque acting on the coil is(a) BinAsin θ(b) (nAi/B) sin θ(c) BinAcos θ (d) Bin2 Acos θ
Answer» Correct Answer is: (c) BinAcos θ

Discussion

108.	A flat circular coil of n turns and radius r carries a current i. Its magnetic moment is(a) πr2ni(b) 2πrni(c) μ0 (ni / 2πr)(d) μ0πr2ni
Answer» Correct Answer is: (a) πr²ni

Discussion

109.	An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude(a) zero(b) μ0ne/2πr(c) μ0ne/2r(b) μ0n2e/2r
Answer» Correct Answer is: (c) μ₀ne/2r The charge flowing past any point on the orbital path per second is ne. This is the equivalent orbital current.

109.

An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude(a) zero(b) μ0ne/2πr(c) μ0ne/2r(b) μ0n2e/2r

Answer»

Correct Answer is: (c) μ₀ne/2r

The charge flowing past any point on the orbital path per second is ne. This is the equivalent orbital current.

Discussion

110.	The adjacent diagram shows a small magnet placed near a solenoid. When current is switched on in the solenoid, will the magnet be attracted or repelled? Give a reason for your answer.
Answer» The magnet will be REPELLED as current flowing is ANTI CLOCK-WISE and N-pole is formed near magnet.

Discussion

111.	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.

111.

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.

Discussion

112.	For the solenoid given in the diagram name the polarities A and B of a solenoid when the current flows in the direction shown.A) North and south B) South and north C) East and west D) West and east
Answer» A) North and south

Discussion

113.	In what form is the energy in a current carrying coil stored?
Answer» It is stored in the form of magnetic field.

Discussion

114.	Which is not the property of a solenoid? The magnetic field of solenoid can be increased (a) by increasing the number of turns in the solenoid. (b) by increasing the strength of current flowing through the solenoid. (c) by placing a stainless steel core within the solenoid. (d) by placing a laminated soft iron core within the solenoid.
Answer» (c) by placing a stainless steel core within the solenoid.

Discussion

115.	Which of the following statements is aretrue ? A) The direction of the magnetic field lines due to straight current carrying wire can be determined by using right hand rule. B) The direction of the magnetic field lines due to circular current carrying wire can be determined by using right hand rule. C) The direction of the magnetic field lines due to current carrying solenoid can be determined by using right hand rule. D) All of the above
Answer» D) All of the above

Discussion

116.	What is solenoid?
Answer» A solenoid is a long wire wound in a close packed helix.

Discussion

117.	List any two properties of magnetic field lines.
Answer» 1. Inside the magnet they start from south pole and end at north pole whereas outside the magnet they start at north pole and end at south pole. 2. Two magnetic lines of force never intersect each other.

117.

List any two properties of magnetic field lines.

Answer»

1. Inside the magnet they start from south pole and end at north pole whereas outside the magnet they start at north pole and end at south pole.

2. Two magnetic lines of force never intersect each other.

Discussion

118.	Explain why on increasing the number of turs per unit length in a solenoid, the magnetic field strength increases.
Answer» What happens to the total length of the wire when the number of turns per unit length is increased. What are the factors affecting the strength of the magnetic field and how are they related ?

Discussion

119.	What is the pattern of field lines inside a solenoid around when current carrying solenoid?
Answer» Parallel to each other.

Discussion

120.	Statement X : The strength of the magnetic field inside a solenoid is the same at all the points. Statement Y : The strength of the magnetic field is the same at all points outside the solenoid. A) Both statements are true B) Both statements are false C) X is true, Y is falseD) X is false, Y is true
Answer» C) X is true, Y is false

Discussion

121.	The magnetic field lines inside a current carrying solenoid, are (a) along the axis and are parallel to each other (b) perpendicular to the axis and equidistant from each other (c) circular and do not intersect each other (d) circular at the ends but they are parallel to the axis inside the solenoid.
Answer» (a) along the axis and are parallel to each other

Discussion

122.	Magnetic field lines inside a solenoidA. are parallel to each otherB. are convergentC. are divergentD. None of the above
Answer» Correct Answer - A

Discussion

123.	A current passes from south to north, through a conductor placed in a horizontal position. If a magnetic needle is placed horizontally below the conductor then it woud deflect towardsA. westB. eastC. southD. north
Answer» Correct Answer - A

Discussion

124.	A 5 MeV proton moves vertically downward through a magnetic field of induction `1.5 "weber"//m^(2)` pointing horizontally from south to north. The force acting on the proton, mass of proton `= 1.6 × 10–27 kg`. will be A. `7.44 xx 10^(-12)N`B. `3.1 xx 10^(-12) N`C. `5 xx 10^(-12) N`D. `6 xx 10^(-12) N`
Answer» Correct Answer - A

Discussion

125.	A conductor rod AB moves parallel to X-axis in a uniform magnetic field, pointing in the positive Z-direction. The end A of the rod gets- A. positively chargedB. negatively chargedC. neutralD. first positively charged and then negatively charged.
Answer» Correct Answer - B

Discussion

126.	Statement X : When a current carrying wire is kept perpendi-cular to the magnetic field it experiences a force. Statement Y : When a current carrying wire is kept along the direction (or) against the direction of magnetic field it experiences no force. A) Both statements are true B) Both statements are false C) X is true, Y is false D) X is false, Y is true
Answer» A) Both statements are true

Discussion

127.	As shown in the figure a positive charge ‘q’ moves at a speed ‘v’ in a constant uniform magnetic field directed into the page. The direction of velocity is perpendicular to the direction of magnetic field. The direction of magnetic force on the charge ‘q’ is …………………A) due north B) due south C) due west D) due east
Answer» A) due north

Discussion

128.	As shown in figure, both coil and bar magnet move in the same direction. Your friend is arguing that there is no change in flux. Do you agree with his statement? If not, what doubts do you have? Frame questions about the doubts you have regarding change in flux.
Answer» What happens if both magnet and coil move in same direction? What happens if both magnet and coil move in opposite direction? What is the direction of the current in the coil? If both move in same direction, is there any linkage of flux with the coil? When ‘N’ pole is moved towards the coil what is the direction of current? If magnet is reversed, what is the direction of current in the coil?

Discussion

129.	Why is earthing of electrical appliances recommended?
Answer» To protect the user from any accidental electrical shock caused due to leakage of current.

Discussion

130.	At what voltage is this current available to our household?
Answer» The current is available to our household at a voltage of 220V.

Discussion

131.	Why does a current carrying freely suspended solenoid rest along a particular direction.
Answer» A current-carrying freely suspended solenoid acts as a bar mag net, and thus, due to the Earth’s magnetic field, it rests along a particular direction.

Discussion

132.	What could be the reason for that?
Answer» It is due to the magnetic field produced by electric charges in motion.

Discussion

133.	Why does the picture get distorted?
Answer» Due to motion of electrons that form the picture is affected by the magnetic field of bar magnet.

Discussion

134.	Why does the picture appear distorted when a bar magnet is brought close to the screen of a television? Explain. (OR) Explain magnetic force on moving charge and current carrying wire. (OR) What happens when you bring a bar magnet near a picture of TV screen ? What inference do you conclude from this activity?
Answer» This is due to the fact that magnetic field exerts a force on the moving charge. TV screen Activity : Take a bar magnet and bring it near the TV screen. Then the picture on the screen is distorted. Here the distortion is due to the motion of the electrons reaching the screen are affected by the magnetic field. Now move the bar magnet away from the screen. Then the picture on the screen stabilizes. This must be due to the fact that the magnetic field exerts a force on the moving charges. This force is called magnetic force. The magnitude of the force is F = Bqv where B is magnetic induction, ‘q’ is the charge and v is the velocity of the charged particle

134.

Why does the picture appear distorted when a bar magnet is brought close to the screen of a television? Explain. (OR) Explain magnetic force on moving charge and current carrying wire. (OR) What happens when you bring a bar magnet near a picture of TV screen ? What inference do you conclude from this activity?

Answer»

This is due to the fact that magnetic field exerts a force on the moving charge.

TV screen Activity :

Take a bar magnet and bring it near the TV screen.
Then the picture on the screen is distorted.
Here the distortion is due to the motion of the electrons reaching the screen are affected by the magnetic field.
Now move the bar magnet away from the screen.
Then the picture on the screen stabilizes.
This must be due to the fact that the magnetic field exerts a force on the moving charges. This force is called magnetic force.
The magnitude of the force is F = Bqv where B is magnetic induction, ‘q’ is the charge and v is the velocity of the charged particle

Discussion

135.	The equation for magnetic force on a current carrying wire of length T/ which is placed perpendicular to a magnetic field is …………………. A) F = BILB) F = BIL sinθ C) F = BIL cosθ D) zero
Answer» Correct option is A) F = BIL

Discussion

136.	How can you verify that a current carrying wire produces a magnetic field with the help of an experiment?
Answer» Experiment: Take a thermocole sheet and fix two thin wooden sticks of height 1cm. These sticks are joined with the help of a copper wire. Connect battery and tap key to this copper wire. Place a magnetic compass beneath the wire. Now press the tap key and allow the current through the wire. It is observed that magnetic needle deflects. If you change the direction of the current, the direction of deflection of needle also changes. So we can say current carrying conductor produces magnetic field.

136.

How can you verify that a current carrying wire produces a magnetic field with the help of an experiment?

Answer»

Experiment:

Take a thermocole sheet and fix two thin wooden sticks of height 1cm.
These sticks are joined with the help of a copper wire.
Connect battery and tap key to this copper wire.
Place a magnetic compass beneath the wire.
Now press the tap key and allow the current through the wire. It is observed that magnetic needle deflects.
If you change the direction of the current, the direction of deflection of needle also changes.
So we can say current carrying conductor produces magnetic field.

Discussion

137.	The equation for magnetic force on a current carrying wire of length T/ which makes an angle ‘θ’ with the magnetic field is ………………. A) F = BIL B) F = BIL sinθ C) F = BIL cosθ D) zero
Answer» B) F = BIL sinθ

Discussion

138.	What is the force on the wire if its length makes an angle ‘θ’ with the magnetic field?
Answer» F = Bqv sin θ or F = Bil sin θ, where ‘i’ is current. Here B = magnetic induction, q = charge, v = velocity of the charge and ‘θ’ is the angle between direction of field and velocity.

138.

What is the force on the wire if its length makes an angle ‘θ’ with the magnetic field?

Answer»

F = Bqv sin θ or F = Bil sin θ, where ‘i’ is current.

Here B = magnetic induction, q = charge, v = velocity of the charge and ‘θ’ is the angle between direction of field and velocity.

Discussion

139.	How could you find its (current carrying wire) direction?
Answer» We can find by using right hand rule.

Discussion

140.	What is meant by electromagnetic induction?
Answer» Whenever there is continuous change of magnetic flux linked with a closed coil, current generated in the coil is called electromagnetic induction.

Discussion

141.	The potential of a charged drop is v. This is divided into n smaller drops, then each drop will have the potential as ,A. `n^(-1)v`B. `n^(2//3)v`.C. `n^(3//2)v`D. `n^(-2//3)v`
Answer» Correct Answer - D 135

Discussion

142.	If DC is used, the metal ring lifts up and falls down immediately. Why?
Answer» The flux linked with metal ring is zero. When the switch is on, at that instant there should be a change in the flux linked with ring. So the ring rises up and falls down. If the switch is off, the metal ring again raises up and falls down. There is no change in flux linked with ring when the switch is off.

Discussion

143.	What is responsible for the current in the metal ring?
Answer» The field through the metal ring changes so that flux linked with the metal ring changes and this is responsible for the current in metal ring.

Discussion

144.	What force supports the ring against gravity when it is being levitated?
Answer» The magnetic force developed in the coil of copper wire supports the ring against gravity when it is being levitated.

Discussion

145.	Could the ring be levitated if DC is used?
Answer» The metal ring is levitated because the net force on it should be zero according to Newton’s second law.

Discussion

146.	What is the use of slip – ring in AC motor?
Answer» Uses of slip rings : Slip rings are used to change the direction of current in the coil continuously.

146.

What is the use of slip – ring in AC motor?

Answer»

Uses of slip rings :

Slip rings are used to change the direction of current in the coil continuously.

Discussion

147.	Calculate the reading of voltmeter between X and Y then `(V_(x)-V_(y))` is equal to - A. `10 V`B. `13.33 V`C. `3.33 V`D. `10.33 V`
Answer» Correct Answer - C

Discussion

148.	The two ends of a horizontal conducting rod of length l are joined to a voltmeter. The whole arrangement moves with a horizontal velocity v, the direction of motion being perpendicular to the rod. The vertical component of the earth’s magnetic field is B. The voltmeter reading is(a) Blv only if the rod moves eastward (b) Blv only if the rod moves westward (c) Blv if the rod moves in any direction (d) zero
Answer» Correct Answer is: (d) zero The voltmeter joined to the two ends of a rod forms a closed loop.

148.

The two ends of a horizontal conducting rod of length l are joined to a voltmeter. The whole arrangement moves with a horizontal velocity v, the direction of motion being perpendicular to the rod. The vertical component of the earth’s magnetic field is B. The voltmeter reading is(a) Blv only if the rod moves eastward (b) Blv only if the rod moves westward (c) Blv if the rod moves in any direction (d) zero

Answer»

Correct Answer is: (d) zero

The voltmeter joined to the two ends of a rod forms a closed loop.

Discussion

149.	The magnitude of the earth’s magnetic field at the North Pole is B0. A horizontal conductor of length l moves with a velocity v. The direction of v is perpendicular to the conductor. The induced emf is (a) zero, if v is vertical (b) B0lv, if v is vertical (c) zero, if v is horizontal (d) B0lv, if v is horizontal
Answer» Correct Answer is: (a) zero, if v is vertical, (d) B₀lv, if v is horizontal At the poles, the earth’s magnetic field is vertical.

149.

The magnitude of the earth’s magnetic field at the North Pole is B0. A horizontal conductor of length l moves with a velocity v. The direction of v is perpendicular to the conductor. The induced emf is (a) zero, if v is vertical (b) B0lv, if v is vertical (c) zero, if v is horizontal (d) B0lv, if v is horizontal

Answer»

Correct Answer is: (a) zero, if v is vertical, (d) B₀lv, if v is horizontal

At the poles, the earth’s magnetic field is vertical.

Discussion

150.	…………….. current has some frequency A) A.C B) D.C C) A.C & D.C D) none
Answer» Correct option is A) A.C

Discussion

Explore topic-wise InterviewSolutions in .

A current of 2 ampere is flowing through a coil of radius 0.1 m and having 10 turns. The magnetic moment of the coil will be :A. `20 A-m^(2)`B. `2A-m^(2)`C. `0.314 A-m^(2)`D. `0.628 A-m^(2)`

An electric current of I ampere is flowing in a long conductor CG as shown in figure. Find the magnitude and direction of magnetic induction at the centre O of circular part. A. `(mu_(0)i)/(8r)`B. `(mu_(0)i)/(4r)`C. `(mu_(0)i)/(16r)`D. `0`

An electric current of I ampere is flowing in a long conductor CG as shown in figure. Find the magnitude and direction of magnetic induction at the centre O of circular part. A. `(mu_(0)i)/(2r)(1+(1)/(mu)), o.`B. `0`C. `(mu_(0)i)/(2r)(1-(1)/(mu)), ox`D. `(mu_(0)i)/(2r),o.`

A flat coil of n turns, area A and carrying a current i is placed in a uniform magnetic field of magnitude B. The plane of the coil makes an angle θ with the direction of the field. The torque acting on the coil is(a) BinAsin θ(b) (nAi/B) sin θ(c) BinAcos θ (d) Bin2 Acos θ

A flat circular coil of n turns and radius r carries a current i. Its magnetic moment is(a) πr2ni(b) 2πrni(c) μ0 (ni / 2πr)(d) μ0πr2ni

An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude(a) zero(b) μ0ne/2πr(c) μ0ne/2r(b) μ0n2e/2r

The adjacent diagram shows a small magnet placed near a solenoid. When current is switched on in the solenoid, will the magnet be attracted or repelled? Give a reason for your answer.

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?

For the solenoid given in the diagram name the polarities A and B of a solenoid when the current flows in the direction shown.A) North and south B) South and north C) East and west D) West and east

In what form is the energy in a current carrying coil stored?

What is solenoid?

List any two properties of magnetic field lines.

Explain why on increasing the number of turs per unit length in a solenoid, the magnetic field strength increases.

What is the pattern of field lines inside a solenoid around when current carrying solenoid?

Magnetic field lines inside a solenoidA. are parallel to each otherB. are convergentC. are divergentD. None of the above

A current passes from south to north, through a conductor placed in a horizontal position. If a magnetic needle is placed horizontally below the conductor then it woud deflect towardsA. westB. eastC. southD. north

A conductor rod AB moves parallel to X-axis in a uniform magnetic field, pointing in the positive Z-direction. The end A of the rod gets- A. positively chargedB. negatively chargedC. neutralD. first positively charged and then negatively charged.

As shown in figure, both coil and bar magnet move in the same direction. Your friend is arguing that there is no change in flux. Do you agree with his statement? If not, what doubts do you have? Frame questions about the doubts you have regarding change in flux.

Why is earthing of electrical appliances recommended?

At what voltage is this current available to our household?

Why does a current carrying freely suspended solenoid rest along a particular direction.

What could be the reason for that?

Why does the picture get distorted?

The equation for magnetic force on a current carrying wire of length T/ which is placed perpendicular to a magnetic field is …………………. A) F = BILB) F = BIL sinθ C) F = BIL cosθ D) zero

How can you verify that a current carrying wire produces a magnetic field with the help of an experiment?

The equation for magnetic force on a current carrying wire of length T/ which makes an angle ‘θ’ with the magnetic field is ………………. A) F = BIL B) F = BIL sinθ C) F = BIL cosθ D) zero

What is the force on the wire if its length makes an angle ‘θ’ with the magnetic field?

How could you find its (current carrying wire) direction?

What is meant by electromagnetic induction?

The potential of a charged drop is v. This is divided into n smaller drops, then each drop will have the potential as ,A. `n^(-1)v`B. `n^(2//3)v`.C. `n^(3//2)v`D. `n^(-2//3)v`

If DC is used, the metal ring lifts up and falls down immediately. Why?

What is responsible for the current in the metal ring?

What force supports the ring against gravity when it is being levitated?

Could the ring be levitated if DC is used?

What is the use of slip – ring in AC motor?

Calculate the reading of voltmeter between X and Y then `(V_(x)-V_(y))` is equal to - A. `10 V`B. `13.33 V`C. `3.33 V`D. `10.33 V`

…………….. current has some frequency A) A.C B) D.C C) A.C &amp; D.C D) none

…………….. current has some frequency A) A.C B) D.C C) A.C & D.C D) none