Deck 8: Magnetic Induction

Question 1

A circular wire coil of radius 25 cm and 20 turns is sitting in a perpendicular magnetic field of 0.2 T. If the coil is flipped over, what is the change in magnetic flux through the loop?

A) 0 Wb
B) 1.6 Wb
C) 0.080 Wb
D) 0.80 Wb
E) 0.040 Wb

Answer 1

1.6 Wb

Question 2

The magnetic flux through a 50-cm-long solenoid that has 500 turns of radius 3.0 cm is 3.0 *10^-2 Wb. Calculate the current through the solenoid.

A) 53 A
B) 5.4 A
C) 17 A
D) 1.3 A
E) 34 A

Answer 2

17 A

Question 3

A uniform magnetic field of magnitude 0.5 T is parallel to the x axis. A square coil of side 10 cm has 300 turns and makes an angle of 60º with the z axis as shown. The magnetic flux through the coil is approximately

A) 0.14 Wb
B) 0.75 Wb
C) 1.5 Wb
D) 0.27 Wb
E) 0.56 Wb

Answer 3

0.75 Wb

Question 4

A uniform magnetic field of 0.5 T is parallel to the z axis. A square coil of side 10 cm has 300 turns and lies in the xy plane as shown. The magnetic flux through the coil is

A) 0.14 Wb
B) 0.75 Wb
C) 1.5 Wb
D) 0.27 Wb
E) zero

Question 5

Suppose you double the magnetic field in a given region and quadruple the area through which this magnetic field exists. The effect on the flux through this area would be to

A) leave it unchanged.
B) double it.
C) quadruple it.
D) increase it by a factor of six.
E) increase it by a factor of eight.

Question 6

A 3.0-cm by 5.0-cm rectangular coil has 100 turns. Its axis makes an angle of 55º with a uniform magnetic field of 0.35 T. What is the magnetic flux through this coil?

A) 3.0*10^-4 Wb
B) 4.3 * 10^-4 Wb
C) 3.0 * 10^-2 Wb
D) 4.3 *10^-2 Wb
E) 5.3 * 10^-2 Wb

Question 7

Use the following figure for the next two problems.

-A rectangle is bent on two sides at 90 $\degree$ so that one end lies along the xy-plane while the other end lies along the xz-plane. The length a = 10 cm and b = 30 cm. At t = 0, a magnetic field of strength B = 0.1 T lies in the yz-plane and points at an angle $\theta$ = 30 $\degree$ and 10 ms later the field points in the opposite direction. The EMF induced in the rectangle is

A) 10.4 V
B) 6.0 V
C) 12 V
D) 8.2 V
E) None of these is correct.

Question 8

A long straight wire carries a constant current I. The magnitude of the magnetic flux through the illustrated rectangular loop of wire is

A) ( $\mu$ ₀/4 $\pi$ )2Il ln(b/a)
B) ( $\mu$ ₀/4 $\pi$ )4Il ln(b/a)
C) ( $\mu$ ₀/4 $\pi$ )Il ln[(a + b)/(b - a)]
D) ( $\mu$ ₀/4 $\pi$ )4Il ln[(b - a)/(b + a)]
E) ( $\mu$ ₀/4 $\pi$ )2Il ln[(b - a)/(b + a)]

Question 9

A rectangular loop of wire (0.10 m by 0.20 m) carries a current of 5.0 A in a counterclockwise direction. The loop is oriented, as shown, in a uniform magnetic field of 1.5 T. The magnetic flux of is

A) 0.026 T · m²
B) 1.3 T · m²
C) 0.015 T · m²
D) 0.030 T · m²
E) 1.5 T · m²

Question 10

A solenoid 50 cm long with a radius of 5.0 cm has 800 turns. You find that it carries a current of 10 A. The magnetic flux through it is approximately

A) 47 mWb
B) 31 mWb
C) 98 mWb
D) 18 mWb
E) 67 mWb

Question 11

A square loop of sides a lies in the yz plane with one corner at the origin. A varying magnetic field where k is a constant, passes through the loop. The magnetic flux through the loop is

A) ka²
B) ka²/2
C) ka³/2
D) ka³/3
E) None of these is correct.

Question 12

A rectangular surface of area 1.0 m² is hinged along the z axis and makes an angle of 37º with the yz plane. If the local magnetic field is 10 T , the magnetic flux through this surface is

A) 6.0 T · m²
B) 8.0 T · m²
C) 10 T · m²
D) 13 T · m²
E) 17 T · m²

Question 13

The magnetic flux through a loop is made to vary according to the relation
$\phi$ _m = 6t² + 7t + 1
Where the units are SI. The EMF induced in the loop when t = 2 s is

A) 38 V
B) 39 V
C) 40 V
D) 31 V
E) 19 V

Question 14

Use the following figure for the next two problems.

-A rectangle is bent on two sides at 90 $\degree$ so that one end lies along the xy plane while the other end lies along the xz plane. The length a = 10 cm and b = 30 cm. A magnetic field of strength B = 0.1 T lies in the yz plane and points at an angle $\theta$ = 30 $\degree$ with the y axis. The flux through the rectangle is

A) 52.0 mWb
B) 30.0 mWb
C) 41.0 mWb
D) 60.0 mWb
E) None of these is correct.

Question 15

A uniform magnetic field of 0.5 T is parallel to the y axis. A square coil of side 10 cm has 300 turns and lies in the xy plane as shown. The magnetic flux through the coil is

A) 0.14 Wb
B) 0.75 Wb
C) 1.5 Wb
D) 0.27 Wb
E) None of these answers is correct.

Question 16

You can change the magnetic flux through a given surface by

A) changing the magnetic field.
B) changing the surface area over which the magnetic field is distributed.
C) changing the angle between the magnetic field and surface in question.
D) any combination of a through c.
E) none of these strategies.

Question 17

The magnetic flux through a certain coil is given by
$\phi$ _m = (1/50 $\pi$ ) cos 100 $\pi$ t
Where the units are SI. The coil has 100 turns. The magnitude of the induced EMF when t = 1/200 s is

A) 100 V
B) 200 V
C) zero
D) 2/ $\pi$ V
E) 1/50 $\pi$ V

Question 18

A uniform magnetic field of 0.5 T is parallel to the x axis. A square coil of side 10 cm has 300 turns and lies in the xy plane as shown. The magnetic flux through the coil is

A) 0.14 Wb
B) 0.75 Wb
C) 1.5 Wb
D) 0.27 Wb
E) zero

Question 19

Which of the following is a vector quantity?

A) current
B) charge
C) magnetic field
D) electric potential
E) magnetic flux

Question 20

For which of the following diagram(s) will current flow through the light bulb?

A) 1
B) 2
C) 3
D) 4
E) 1 and 2

Question 21

A conducting loop around a bar magnet begins to move away from the magnet. Which of the following statements is true?

A) The magnet and the loop repel one another.
B) The magnet and the loop attract one another.
C) The magnet is attracted, but the loop is repelled.
D) The magnet is repelled, but the loop is attracted.
E) The magnet and loop neither attract nor repel one another.

Question 22

A circular loop of radius 25 cm is sitting in a perpendicular magnetic field of 0.2 T. If the magnetic field strength changes to a value of 0.5 T in 2.5 s, calculate the induced EMF in the loop.

A) 7.5 * 10^-3 V
B) 9.6 * 10^-2 V
C) 4.0 * 10^-2 V
D) 2.4*10^-2 V
E) none of the above

Question 23

A copper ring lies in the yz plane as shown. The magnet's long axis lies along the x axis. Induced current flows through the ring as indicated. The magnet

A) must be moving away from the ring.
B) must be moving toward the ring.
C) must be moving either away from or toward the ring.
D) is not necessarily moving.
E) must remain stationary to keep the current flowing.

Question 24

The instantaneous induced EMF in a coil of wire located in a magnetic field

A) depends on the time rate of change of flux through the coil.
B) depends on the instantaneous value of flux through the coil.
C) is independent of the area of the coil.
D) is independent of the number of turns of the coil.
E) is determined by the resistance in series with the coil.

Question 25

The plane of a circular, 200-turn coil of radius 5.25 cm is perpendicular to a uniform magnetic field produced by a large electromagnet. This field is changed at a steady rate from 0.650 T to 0.150 T in 0.0100 s. What is the magnitude of the EMF induced in the coil?

A) 110 V
B) 170 V
C) 1.7 V
D) 26 V
E) 87 V

Question 26

A 3.0-cm by 5.0-cm rectangular coil has 100 turns. Its axis makes an angle of 55º with a uniform magnetic field of 0.35 T. It requires 0.33 s to turn the coil until its plane is perpendicular to the magnetic field. What is the (average) magnitude of the induced EMF?

A) 0.16 V
B) 0.13 V
C) 91 mV
D) 68 mV
E) 29 mV

Question 27

A loop rests in the xy plane. The z axis is normal to the plane and positive upward. The direction of the changing flux is indicated by the arrow on the z axis. The diagram that correctly shows the direction of the resultant induced current in the loop is

A) 1
B) 2
C) 3
D) 4
E) 5

Question 28

The wire is located in a region in which there is a uniform magnetic field in the y direction. You note that the induced EMF in the wire is zero. From this observation, you can conclude that

A) it must be moving in the z direction.
B) it must be moving in the -z direction.
C) it must be at rest or moving parallel to the magnetic field.
D) it must be moving in such a way that its velocity vector makes an angle other than zero with .
E) All of these are correct.

Question 29

A square coil of wire with side 9.0 cm and 8 turns sits in a uniform magnetic field of 2 T that is perpendicular to the plane of the coil. If an EMF of 0.5 V is induced in the coil when the magnetic field is reversed, find the time taken for the field reversal.

A) 0.26 s
B) 1.0 s
C) 5.8 s
D) 1.6 s
E) 0.52 s

Question 30

A circular loop of radius R has 50 turns. It lies in the xy plane. A time dependent magnetic field where A is a constant, passes through the loop. The EMF induced in the loop is

A) 50 $\pi$ AR² sin ( $\omega$ t)
B) 50 $\pi$ AR² cos ( $\omega$ t)
C) 50 $\pi$ $\omega$ AR² sin ( $\omega$ t)
D) 50 $\pi$ $\omega$ AR² cos ( $\omega$ t)
E) None of these is correct.

Question 31

A square coil of wire with side 8.0 cm and 50 turns sits in a uniform magnetic field that is perpendicular to the plane of the coil. The coil is pulled quickly out of the magnetic field in 0.2 s. If the resistance of the coil is 15 ohm and a current of 12 mA is induced in the coil, calculate the value of the magnetic field.

A) 5.6 T
B) 0.11 T
C) 7.5 * 10^-3 T
D) 1.4 T
E) 9.1 T

Question 32

A wire rod rolls with a speed of 20 m/s on two metallic rails, 1.0 m apart, that form a closed loop. If the magnetic field is 1.5 T into the page, the power dissipated in the resistor R and the current direction are, respectively,

A) 33 mW, clockwise.
B) 33 mW, counterclockwise.
C) 76 mW, counterclockwise.
D) 76 mW, clockwise.
E) 50 mW, clockwise.

Question 33

A bar magnet is dropped through a loop of copper wire as shown. Recall that magnetic field lines point away from a north pole and toward a south pole. If the positive direction of the induced current I in the loop is as shown by the arrows on the loop, the variation of I with time as the bar magnet falls through the loop is illustrated qualitatively by which of the following graphs? The time when the midpoint of the magnet passes through the loop is indicated by C.

A) 1
B) 2
C) 3
D) 4
E) 5

Question 34

Which law does the following statement express? "In all cases of electromagnetic induction, the induced voltages have a direction such that the currents they produce oppose the effect that produces them."

A) Maxwell's law
B) Fleming's rule
C) Lenz's law
D) Gauss's law
E) Ampère's law

Question 35

For which of the following diagrams will current flow in the clockwise direction?

A) 1 and 2
B) 3 and 4
C) 1 and 3
D) 2 and 4
E) 2 and 3

Question 36

According to Faraday's law, a necessary and sufficient condition for an electromotive force to be induced in a closed circuit loop is the presence in the loop of

A) a magnetic field.
B) magnetic materials.
C) an electric current.
D) a time-varying magnetic flux.
E) a time-varying magnetic field.

Question 37

You place a coil that has 200 turns and a cross-sectional area of 0.050 m² so that its plane is normal to a field of 3.0 T. If the field is uniformly decreased to zero in 5.0 s, what EMF is induced in the coil?

A) 0.15 kV
B) 0.12 kV
C) 6.0 V
D) 50 mV
E) 10 mV

Question 38

A 100-turn coil has a radius of 7.50 cm and a resistance of 50.0 $\Omega$ . At what rate must a perpendicular magnetic field change to produce a current of 5.00 A in the coil?

A) 275 T/s
B) 134 T/s
C) 329 T/s
D) 141 T/s
E) 106 T/s

Question 39

A wire rod rolls with a speed of 8.0 m/s on two metallic rails, 30 cm apart, that form a closed loop. A uniform magnetic field of magnitude 1.20 T is into the page. The magnitude and direction of the current induced in the resistor R are

A) 0.82 A, clockwise.
B) 0.82 A, counterclockwise.
C) 1.2 A, clockwise.
D) 1.2 A, counterclockwise.
E) 2.9 A, counterclockwise.

Question 40

A wire rod rolls with a speed of 30 m/s on two metallic rails, 2.0 m apart, that form a closed loop. The power dissipated in the resistor R and the current direction are, respectively,

A) 33 mW, clockwise.
B) 33 mW, counterclockwise.
C) 2.0 W, counterclockwise.
D) 10 W, clockwise.
E) 10 W, counterclockwise.

Question 41

Use the following figure for the next three problems.
A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left. While the coil is entering the field, the direction of the magnetic force is

A) 1
B) 2
C) 3
D) 4
E) 5

Question 42

A coil with a self-inductance of 6.5 H carries a current that is changing at a rate of
50 A/s. What is the induced EMF in the coil?

A) 0.13 V
B) 7.7 V
C) 32 V
D) 65 V
E) 0.32 kV

Question 43

The motion of a conducting rod through a magnetic field creates a motional EMF E. If the rod accelerates to twice the speed, what will the motional EMF be?

A) $\varepsilon$
B) 2 $\varepsilon$
C) $\varepsilon$ /2
D) 4 $\varepsilon$
E) $\varepsilon$ ²

Question 44

Use the following figure for the next three problems.
A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left. While the coil is exiting the field on the right, the direction of the magnetic force is

A) 1
B) 2
C) 3
D) 4
E) 5

Question 45

Use the following figure for the next two problems:
A classic demonstration illustrating eddy currents is performed by dropping a permanent magnet inside a conducting cylinder. The magnet does not go into free fall. Instead it reaches terminal velocity and can take a few seconds to drop a length of about a meter. Suppose the mass of the magnet is 70 g and it has a terminal velocity of 10 cm/s. The length of the pipe is 80 cm. What is the magnitude of the magnetic force on the magnet when it is falling at the terminal velocity?

A) 0.35 N
B) 0.79 N
C) 0.97 N
D) 0.69 N
E) None of these is correct.

Question 46

A 0.8-m-long pole rotates about a perpendicular axis at one end. As the pole rotates, it passes through Earth's magnetic field, which has a perpendicular component of 3 *10^-5 T to the plane of rotation. If the pole rotates with a frequency of 5 revolutions per second, calculate the induced EMF across the ends of the pole.

A) 3.0*0^-4 V
B) 1.2 *10^-5 V
C) 1.0 * 10^-4 V
D) 3.8 *10^-4 V
E) 2.4* 10^-4 V

Question 47

What is the average induced EMF between the ends of the wings of a plane flying at a speed of 500 km/hr when the vertical component of Earth's magnetic field is
3 * 10^-5 T? The distance between the wingtips is 25 m.

A) 0.20 V
B) 0.050 V
C) 6.0 V
D) 0.10 V
E) none of the above

Question 48

Use the following figure for the next two problems:

-A classic demonstration illustrating eddy currents is performed by dropping a permanent magnet inside a conducting cylinder. The magnet does not go into free fall. Instead it reaches terminal velocity and can take a few seconds to drop a length of about a meter. Suppose the mass of the magnet is 70 g and width of 1.0 cm. It falls with a terminal velocity of 10 cm/s and the length of the pipe is 80 cm. The magnitude of the Joule heating from the eddy currents is approximately

A) 0.55 J
B) 8.8 * 10^-5 J
C) 1.1 J
D) 1.8 *10^-4 J
E) None of these is correct.

Question 49

The plane of a wire loop with an area of 0.20 m² is perpendicular to a magnetic field of 50 mT. In 40 ms you rotate the loop 90º so that its plane is parallel to the magnetic field. The average EMF induced in the loop is

A) 0.25 V
B) 6.0 V
C) 3.0 V
D) 4.0 V
E) 1.3 V

Question 50

A straight conductor 10 cm long is perpendicular to a uniform magnetic field of flux density 2.0 mT. When the conductor carries a current of 5.0 A, the force exerted on it by the field is

A) 0.25 kN
B) 40 $\mu$ N
C) 1.0 mN
D) zero
E) 5.0 mN

Question 51

Two identical bar magnets are dropped from equal heights. Magnet A is dropped over bare earth and magnet B over a metal plate. Which magnet strikes first?

A) magnet A
B) magnet B
C) both strike at the same time
D) whichever has its N pole toward the ground
E) whichever has its S pole toward the ground

Question 52

A metal disk rotates about its central axis at an angular frequency of 800 radians per second in a uniform magnetic field of 0.8 T. The diameter of the disk is 8 cm. What is the magnitude of the voltage difference between the center and edge of the disk?

A) 0 V
B) 0.80 V
C) 0.51 V
D) 1.0 V
E) 3.1 V

Question 53

A coil consisting of 20 turns of wire around the periphery of a rectangular frame 10 cm by 5.0 cm is moved from a position near a magnet where the average flux density is
1)0 mT to another position where the average is 11 mT. If this motion takes place in
1)0 s, the average EMF induced in the coil is

A) 0.10 kV
B) 1.0 kV
C) 1.0 mV
D) 0.10 MV
E) 10 mV

Question 54

You place a single loop of wire 0.50 m by 0.30 m perpendicular to a field of 2.0 T. In 30 ms you turn the loop until it is parallel with the field. The average emf induced in this loop is

A) 0.30 V
B) 10 V
C) 5.0 V
D) 67 V
E) 20 V

Question 55

A 0.1-m-long rod rotates about a perpendicular axis at one end. As the rod rotates, it passes through a uniform magnetic field that has a perpendicular component of 3 *10^-2 T to the plane of rotation. If the induced EMF across the ends of the rod is
0)2 V, then calculate the number of revolutions per second of the rod.

A) 6.7 * 10¹ revs/s
B) 6.7 *10³ revs/s
C) 4.7*10^-3 revs/s
D) 6.7*10² revs/s
E) 2.1 *10² revs/s

Question 56

A circular loop, of radius 15 cm and negligible resistance, is sitting in a perpendicular magnetic field of 0.1 T. If the magnetic field strength changes to a value of 0.5 T in
0)5 s, calculate the induced current in the loop if it is in series with a 20 ohm resistor.

A) 5.7*10^-2 A
B) 1.2 * 10^-2 A
C) 2.8 *10^-3 A
D) 6.0 *10^-4 A
E) 1.1 A

Question 57

Eddy currents

A) are a consequence of changing magnetic flux.
B) generate heat and result in power loss.
C) can be used for damping and braking purposes.
D) are described by both Faraday's and Lenz's laws.
E) All of these are correct.

Question 58

For the current in a stationary circuit to induce a current in an independent stationary circuit, it is necessary for the first circuit to have

A) a steady current.
B) a large current.
C) no current.
D) a changing current.
E) None of these is correct.

Question 59

A 25-cm long conducting rod moves at a speed of 12 m/s in a plane perpendicular to a uniform magnetic field of magnitude 0.080 T. What is the induced potential difference between the ends of the rod?

A) 24 V
B) 2.4 V
C) 0.24 V
D) 0.60 kV
E) 6.0 V

Question 60

Use the following figure for the next three problems.

-A rectangular coil of length l = 20 cm and width w = 15 cm is moving at a constant speed v = 5 m/s. It enters a region of uniform magnetic field B = 0.2 T from the left. While the coil is completely immersed in the field, the voltage across points a and b is

A) 0.20 V
B) 0.15 V
C) -0.20 V
D) -0.15 V
E) zero

Question 61

A device used chiefly for storing energy in a magnetic field is

A) an inductor.
B) a resistor.
C) a capacitor.
D) a galvanometer.
E) a dielectric.

Question 62

For the two solenoids above, if l = 50 cm, N₁ = N₂ = 200 turns and r₁ = 5 cm and r₂ = 10 cm, the mutual inductance of the two solenoids is
I

A) 1.58 mH
B) 0.790 mH
C) 3.20 mH
D) 6.31 mH
E) None of these is correct.

Question 63

An LR circuit has a resistance R = 25 $\Omega$ , an inductance L = 5.4 mH, and a battery of EMF = 9.0 V. How much energy is stored in the inductance of this circuit when a steady current is achieved?

A) zero
B) 0.35 J
C) 0.35 mJ
D) 0.70 mJ
E) 0.97 mJ

Question 64

After you measure the self-inductance of a coil, you unwind it and then rewind half the length of wire into a coil with the same diameter but half the number of turns. How does this change the self-inductance?

A) it is the same
B) it is doubled
C) it is quadrupled
D) it is halved
E) it is quartered

Question 65

A coil of self inductance 7.5 mH and resistance of 30 $\Omega$ is placed across the terminals of a 12-V battery of negligible internal resistance. The current in this circuit after 50 $\mu$ s is approximately

A) 73 mA
B) 47 mA
C) 28 mA
D) 51 mA
E) 19 mA

Question 66

An open switch in an RL circuit is closed at time t = 0, as shown. The curve that best illustrates the variation of potential difference across the inductor as a function of time is

A) 1
B) 2
C) 3
D) 4
E) 5

Question 67

How much does the energy stored in an inductor change if the current through the inductor is doubled?

A) it is the same
B) it is doubled
C) it is quadrupled
D) it is halved
E) it is quartered

Question 68

An open switch in an RL circuit is closed at time t = 0, as shown. The curve that best illustrates the variation of potential difference across the resistor as a function of time is

A) 1
B) 2
C) 3
D) 4
E) 5

Question 69

A region of space contains a magnetic field of 500 G and an electric field of
3 * 10⁶ N/C. The electrical energy density in a cubical box of side = 20 cm in this region is

A) 19.9 J/m³
B) 39.8 J/m³
C) 54.8 J/m³
D) 66.9 J/m³
E) 74.6 J/m³

Question 70

A region of space contains a magnetic field of 500 G and an electric field of
3 *10⁶ N/C. The total energy density in a cubical box of side = 20 cm in this region is

A) 19.4 kJ/m³
B) 12.2 kJ/m³
C) 1.03 kJ/m³
D) 66.9 J/m³
E) 24.6 J/m³

Question 71

The current in an RL circuit is zero at time t = 0 and increases to 75% of its final value in 4.5 s. The time constant of this circuit is approximately

A) 6.0 s
B) 12 s
C) 8.7 s
D) 3.3 s
E) 9.8 s

Question 72

What is the time constant of an RL circuit with a resistance R = 25 $\Omega$ and an inductance L = 5.4 mH?

A) 7.4 s
B) 4.6 s
C) 0.14 s
D) 0.22 ms
E) 1.5 ms

Question 73

The growth of current in the inductive circuit in the inset diagram is represented by the curve in the graph. The broken line is tangent to the curve at the origin. The time constant of the circuit is approximately

A) 3.0 ms
B) 2/R ms
C) 0.40 ms
D) 4.0 ms
E) 2.0 ms

Question 74

The current in an RL circuit is zero at time t = 0 and increases to half its final value in 6.0 s. The time constant of this circuit is approximately

A) 6.0 s
B) 12 s
C) 8.7 s
D) 3.0 s
E) 9.8 s

Question 75

How many turns are needed in a solenoid of radius 10 cm and length 20 cm for its self-inductance to be 6.0 H?

A) 30
B) 74
C) 500
D) 550
E) 5500

Question 76

A coil with self-inductance L carries a current I given by I = I₀ sin 2 $\pi$ ft
The graph that describes the self-induced EMF as a function of time is

A) 1
B) 2
C) 3
D) 4
E) 5

Question 77

A region of space contains a magnetic field of 500 G and an electric field of
3 *10⁶ N/C. The magnetic energy density in a cubical box of side = 20 cm in this region is

A) 550 J/m³
B) 670 J/m³
C) 864 J/m³
D) 995 J/m³
E) None of these is correct.

Question 78

The self-inductance of a wire coil is a proportionality constant that relates

A) electric field to current.
B) electric flux to current.
C) magnetic flux to current.
D) magnetic field to current.
E) voltage to current.

Question 79

An open switch in an RL circuit is closed at time t = 0, as shown. The curve that best illustrates the variation of current with time is

A) 1
B) 2
C) 3
D) 4
E) 5

Question 80

A solenoid is 15 cm long, has a radius of 5 cm, and has 400 turns. If it carries a current of 4 A, the magnetic energy stored in the solenoid is

A) 84.2 mJ
B) 0.562 J
C) 3.37 J
D) 12.6 mJ
E) None of these is correct.