Question 1

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

Accepted Answer

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

Question 2

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

Accepted Answer

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

Question 3

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

Accepted Answer

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  
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 4

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.

Accepted Answer

A) 7.5 $\times$ 10-3 V 
B) 9.6 $\times$ 10-2 V 
C) 4.0 $\times$ 10-2 V 
D) 2.4 $\times$ 10-2 V 
E) none of the above 
A) 7.5 $\times$ 10-3 V 
B) 9.6 $\times$ 10-2 V 
C) 4.0 $\times$ 10-2 V 
D) 2.4 $\times$ 10-2 V 
E) none of the above

Question 5

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

Accepted Answer

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$t) 
E) None of these is correct. 
A) 50$\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 6

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

Accepted Answer

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

Question 7

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?

Accepted Answer

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

Question 8

Use the following figure for the next problem.  
-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

Accepted Answer

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

Question 9

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

Accepted Answer

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. 
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 10

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."

Accepted Answer

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

Question 11

Use the following figure for the next problem:  
-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

Accepted Answer

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

Question 12

You can change the magnetic flux through a given surface by

Accepted Answer

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. 
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 13

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

Accepted Answer

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

Question 14

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.

Accepted Answer

A) 5.7 $\times$ 10-2 A 
B) 1.2 $\times$ 10-2 A 
C) 2.8 $\times$ 10-3 A 
D) 6.0 $\times$ 10-4 A 
E) 1.1 A 
A) 5.7 $\times$ 10-2 A 
B) 1.2 $\times$ 10-2 A 
C) 2.8 $\times$ 10-3 A 
D) 6.0 $\times$ 10-4 A 
E) 1.1 A

Question 15

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

Accepted Answer

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

Question 16

Use the following figure for the next problem:  
-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?

Accepted Answer

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

Question 17

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

Accepted Answer

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

Question 18

Which of the following is a vector quantity?

Accepted Answer

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

Question 19

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.

Accepted Answer

A) 5.6 T 
B) 0.11 T 
C) 7.5 $\times$ 10-3 T 
D) 1.4 T 
E) 9.1 T 
A) 5.6 T 
B) 0.11 T 
C) 7.5 $\times$ 10-3 T 
D) 1.4 T 
E) 9.1 T

Question 20

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?

Accepted Answer

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

Exam 28: Magnetic Induction

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 device used chiefly for storing energy in a magnetic field is

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

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 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

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 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?

Use the following figure for the next problem. -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 conducting loop around a bar magnet begins to move away from the magnet.Which of the following statements is true?

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."

You can change the magnetic flux through a given surface by

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

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.

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

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

Which of the following is a vector quantity?

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?

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