Question 1

The basic function of the electric generator is which of the following conversion processes?

Accepted Answer

A) mechanical energy to electrical 
B) electrical energy to mechanical 
C) low voltage to high or vice versa 
D) alternating current to direct 
A) mechanical energy to electrical 
B) electrical energy to mechanical 
C) low voltage to high or vice versa 
D) alternating current to direct

Question 2

A wire loop of radius 0.250 m is placed in a uniform magnetic field of magnitude 0.740 T. The field is directed perpendicular to the plane of the loop. 
-If the field reverses its direction,and its magnitude changes to 0.100 T in time 1.06 s,what is the magnitude of the average induced emf in the loop during this time?

Accepted Answer

A) 156 mV 
B) 119 mV 
C) 185 mV 
D) 741 mV 
A) 156 mV 
B) 119 mV 
C) 185 mV 
D) 741 mV

Question 3

By what factor is the self-inductance of an air solenoid changed if only its number of coil turns,N,is multiplied by five?

Accepted Answer

A) 1/5 
B) 5 
C) 15 
D) 25 
E) 1/25 
A) 1/5 
B) 5 
C) 15 
D) 25 
E) 1/25

Question 4

According to Lenz's law the direction of an induced current in a conductor will be that which tends to produce which of the following effects?

Accepted Answer

A) enhance the effect which produces it 
B) produce a greater heating effect 
C) produce the greatest voltage 
D) oppose the effect which produces it 
A) enhance the effect which produces it 
B) produce a greater heating effect 
C) produce the greatest voltage 
D) oppose the effect which produces it

Question 5

What is the self-inductance in a coil that experiences a 2.30-V induced emf when the current is changing at a rate of 160 A/s?

Accepted Answer

A) 6.96E-1 H 
B) 3.31E-2 H 
C) 160 H 
D) 1.44E-2 H 
E) 3.68E+1 H 
A) 6.96E-1 H 
B) 3.31E-2 H 
C) 160 H 
D) 1.44E-2 H 
E) 3.68E+1 H

Question 6

The wiring in a motor has resistance of 1.2 Ω and produces a back emf of 0.62 V when connected to a 10.3-V battery of negligible resistance.Find the current flow through the motor.

Accepted Answer

A) 9.1 A 
B) 8.6 A 
C) 0.52 A 
D) 8.1 A 
E) 8.0 A 
A) 9.1 A 
B) 8.6 A 
C) 0.52 A 
D) 8.1 A 
E) 8.0 A

Question 7

A coil is rotated in a magnetic field generating an emf given by emf = NBAω sin θ,where θ = ωt.At which angle θ is the emf one-third of its maximum value?

Accepted Answer

A) 0° 
B) 19.5° 
C) 6.4° 
D) 70.5° 
E) 60.0º 
A) 0° 
B) 19.5° 
C) 6.4° 
D) 70.5° 
E) 60.0º

Question 8

Electricity may be generated by rotating a loop of wire between the poles of a magnet.The induced current is greatest when

Accepted Answer

A) the plane of the loop is parallel to the magnetic field. 
B) the plane of the loop is perpendicular to the magnetic field. 
C) the magnetic flux through the loop is a maximum. 
D) the plane of the loop makes an angle of 45° with the magnetic field. 
A) the plane of the loop is parallel to the magnetic field. 
B) the plane of the loop is perpendicular to the magnetic field. 
C) the magnetic flux through the loop is a maximum. 
D) the plane of the loop makes an angle of 45° with the magnetic field.

Question 9

A series circuit contains a 12-V battery,a 3.3-Ω resistor,and a 4.4-mH inductor.If the switch to the battery is closed at t = 0,find the time required for the current in the circuit to reach 63% of its final value.

Accepted Answer

A) 1.3E-3 s 
B) 1.5E-2 s 
C) 7.5E+2 s 
D) 1.6E-2 s 
E) 1.1E-4 s 
A) 1.3E-3 s 
B) 1.5E-2 s 
C) 7.5E+2 s 
D) 1.6E-2 s 
E) 1.1E-4 s

Question 10

An inductor,battery,resistance,and ammeter and switch are connected in series.If the switch,initially open,is now closed,what is the current's final value?

Accepted Answer

A) zero 
B) battery voltage divided by inductance 
C) battery voltage times inductance 
D) battery voltage divided by resistance 
A) zero 
B) battery voltage divided by inductance 
C) battery voltage times inductance 
D) battery voltage divided by resistance

Question 11

How is the energy stored in a current-carrying inductor related to its self-inductance,L?

Accepted Answer

A) directly proportional to L2 
B) directly proportional to L1/2 
C) directly proportional to L 
D) inversely proportional to L 
A) directly proportional to L2 
B) directly proportional to L1/2 
C) directly proportional to L 
D) inversely proportional to L

Question 12

A circular loop (area = 0.20 m2)turns in a uniform magnetic field with B = 0.13 T.At an instant when the angle between the magnetic field and the normal to the plane of the loop is π rads and is decreasing at the rate of 0.50 rad/s,what is the magnitude of the emf induced in the loop?

Accepted Answer

A) zero 
B) 13 mV 
C) 26 mV 
D) 20 mV 
A) zero 
B) 13 mV 
C) 26 mV 
D) 20 mV

Question 13

A bar magnet is held above the center of a conducting ring in the horizontal plane.The magnet is dropped so it falls lengthwise toward the center of the ring.Will the falling magnet be attracted toward the ring or be repelled by the ring due to the magnetic interaction of the magnet and the ring?

Accepted Answer

A) It will be attracted. 
B) It will be repelled. 
C) It will be attracted only if the north end of the magnet is the leading end as it falls toward the ring. 
D) It will be attracted only if the south end of the magnet is the leading end as it falls toward the ring. 
A) It will be attracted. 
B) It will be repelled. 
C) It will be attracted only if the north end of the magnet is the leading end as it falls toward the ring. 
D) It will be attracted only if the south end of the magnet is the leading end as it falls toward the ring.

Question 14

A flat coil of wire consisting of 15 turns,each with an area of 40 cm2,is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 1.5 T to 5.1 T in 2.0 s.If the coil has a total resistance of 0.20 Ω,what is the magnitude of the induced current?

Accepted Answer

A) 7.65E-1 A 
B) 5.40E+1 A 
C) 5.40E-1 A 
D) 8.64E-2 A 
E) 2.16E-1 A 
A) 7.65E-1 A 
B) 5.40E+1 A 
C) 5.40E-1 A 
D) 8.64E-2 A 
E) 2.16E-1 A

Question 15

A straight wire lies along the y-axis initially carrying a current of 10 A in the positive y-direction.The current decreases and reverses to 10 A in the negative y-direction,the change in current happening at a uniform rate.In the 1st quadrant a square conducting coil has 2 sides parallel to the y-axis and the other 2 sides parallel to the x-axis.The side of the coil nearest and parallel to the straight wire is at a distance equal to the length of one of the sides of the square.As the current is going from 10 A in one direction to 10 A in the other,in which direction is the induced current in this side of the square coil nearest to the straight wire?

Accepted Answer

A) It is in the positive y-direction. 
B) It is in the negative y-direction. 
C) At first it is in the positive y-direction,but after the current passes through zero,it is in the negative y-direction. 
D) At first it is in the negative y-direction but after the current passes through zero,it is in the positive y-direction. 
A) It is in the positive y-direction. 
B) It is in the negative y-direction. 
C) At first it is in the positive y-direction,but after the current passes through zero,it is in the negative y-direction. 
D) At first it is in the negative y-direction but after the current passes through zero,it is in the positive y-direction.

Question 16

A planar loop consisting of seven turns of wire,each of which encloses 200 cm2,is oriented perpendicularly to a magnetic field that increases uniformly in magnitude from 14 × 10-3 T to 38 × 10-3 T in a time of 8.0 × 10-3 s.What is the resulting induced current in the coil if the resistance of the coil is 5.0 Ω?

Accepted Answer

A) 1.2E-2 A 
B) 1.2E+0 A 
C) 1.3E-1 A 
D) 8.4E-2 A 
E) 7.7E-1 A 
A) 1.2E-2 A 
B) 1.2E+0 A 
C) 1.3E-1 A 
D) 8.4E-2 A 
E) 7.7E-1 A

Question 17

An RL series circuit has: 4.8-mH coil,2.8-Ω resistor,1.0-V battery,ammeter and switch.After the switch is closed for a long time,find the final value of the current.

Accepted Answer

A) 7.4E+1 A 
B) 3.6E-1 A 
C) 1.3E-2 A. 
D) 2.8E+2 A 
E) 1.3E-2 A 
A) 7.4E+1 A 
B) 3.6E-1 A 
C) 1.3E-2 A. 
D) 2.8E+2 A 
E) 1.3E-2 A

Question 18

A sensitive ammeter is connected to a wire loop and placed within the magnetic field of a strong horseshoe magnet.The ammeter shows a deflection when:

Accepted Answer

A) the wire is moved parallel to the field. 
B) the wire is moved perpendicularly to the field. 
C) neither wire nor magnet is moving. 
D) the wire's axis is parallel to the field. 
A) the wire is moved parallel to the field. 
B) the wire is moved perpendicularly to the field. 
C) neither wire nor magnet is moving. 
D) the wire's axis is parallel to the field.

Question 19

What is the minimum frequency with which a 300-turn,flat coil of cross sectional area 370 cm2 can be rotated in a uniform 25-mT magnetic field if the maximum value of the induced emf is to equal 8.6 V?

Accepted Answer

A) 0.20 Hz 
B) 2.2 Hz 
C) 4.9 Hz 
D) 31 Hz 
E) 0.031 Hz 
A) 0.20 Hz 
B) 2.2 Hz 
C) 4.9 Hz 
D) 31 Hz 
E) 0.031 Hz

Question 20

A coil is placed in a changing magnetic field and an emf is induced.What happens to the induced emf if the rate of change of magnetic field quadruples?

Accepted Answer

A) There is no change. 
B) The emf doubles. 
C) The emf quadruples. 
D) The emf increases by a factor of 16. 
A) There is no change. 
B) The emf doubles. 
C) The emf quadruples. 
D) The emf increases by a factor of 16.

Exam 20: Induced Voltages and Inductance

The basic function of the electric generator is which of the following conversion processes?

By what factor is the self-inductance of an air solenoid changed if only its number of coil turns,N,is multiplied by five?

According to Lenz's law the direction of an induced current in a conductor will be that which tends to produce which of the following effects?

What is the self-inductance in a coil that experiences a 2.30-V induced emf when the current is changing at a rate of 160 A/s?

The wiring in a motor has resistance of 1.2 Ω and produces a back emf of 0.62 V when connected to a 10.3-V battery of negligible resistance.Find the current flow through the motor.

A coil is rotated in a magnetic field generating an emf given by emf = NBAω sin θ,where θ = ωt.At which angle θ is the emf one-third of its maximum value?

Electricity may be generated by rotating a loop of wire between the poles of a magnet.The induced current is greatest when

A series circuit contains a 12-V battery,a 3.3-Ω resistor,and a 4.4-mH inductor.If the switch to the battery is closed at t = 0,find the time required for the current in the circuit to reach 63% of its final value.

An inductor,battery,resistance,and ammeter and switch are connected in series.If the switch,initially open,is now closed,what is the current's final value?

How is the energy stored in a current-carrying inductor related to its self-inductance,L?

A circular loop (area = 0.20 m2)turns in a uniform magnetic field with B = 0.13 T.At an instant when the angle between the magnetic field and the normal to the plane of the loop is π rads and is decreasing at the rate of 0.50 rad/s,what is the magnitude of the emf induced in the loop?

A bar magnet is held above the center of a conducting ring in the horizontal plane.The magnet is dropped so it falls lengthwise toward the center of the ring.Will the falling magnet be attracted toward the ring or be repelled by the ring due to the magnetic interaction of the magnet and the ring?

A flat coil of wire consisting of 15 turns,each with an area of 40 cm2,is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 1.5 T to 5.1 T in 2.0 s.If the coil has a total resistance of 0.20 Ω,what is the magnitude of the induced current?

An RL series circuit has: 4.8-mH coil,2.8-Ω resistor,1.0-V battery,ammeter and switch.After the switch is closed for a long time,find the final value of the current.

A sensitive ammeter is connected to a wire loop and placed within the magnetic field of a strong horseshoe magnet.The ammeter shows a deflection when:

What is the minimum frequency with which a 300-turn,flat coil of cross sectional area 370 cm2 can be rotated in a uniform 25-mT magnetic field if the maximum value of the induced emf is to equal 8.6 V?

A coil is placed in a changing magnetic field and an emf is induced.What happens to the induced emf if the rate of change of magnetic field quadruples?

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A circular loop (area = 0.20 m²)turns in a uniform magnetic field with B = 0.13 T.At an instant when the angle between the magnetic field and the normal to the plane of the loop is π rads and is decreasing at the rate of 0.50 rad/s,what is the magnitude of the emf induced in the loop?

A flat coil of wire consisting of 15 turns,each with an area of 40 cm²,is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 1.5 T to 5.1 T in 2.0 s.If the coil has a total resistance of 0.20 Ω,what is the magnitude of the induced current?

What is the minimum frequency with which a 300-turn,flat coil of cross sectional area 370 cm² can be rotated in a uniform 25-mT magnetic field if the maximum value of the induced emf is to equal 8.6 V?