Question 1

A transformer changes 120 V across the primary to 1200 V across the secondary. If the secondary coil has 800 turns, how many turns does the primary coil have?

Accepted Answer

A) 40 
B) 80 
C) 100 
D) 400 
E) 4000 
A) 40 
B) 80 
C) 100 
D) 400 
E) 4000

Question 2

A flexible, circular conducting loop of radius 0.15 m and resistance 4.0 $\varOmega$ lies in a uniform magnetic field of 0.25 T. The loop is pulled on opposite sides by equal forces and stretched until its enclosed area is essentially zero mS1U1P12S1S1P0, as suggested in the drawings. It takes 0.30 s to close the loop.  
-Determine the magnitude of the emf induced in the loop.

Accepted Answer

A) 1.2 × 10-1 V 
B) 1.8 × 10-2 V 
C) 1.8 × 102 V 
D) 5.9 × 10-2 V 
E) 5.9 × 102 V 
A) 1.2 × 10-1 V 
B) 1.8 × 10-2 V 
C) 1.8 × 102 V 
D) 5.9 × 10-2 V 
E) 5.9 × 102 V

Question 3

A 0.100-m long solenoid has a radius of 0.050 m and 1.50 × 10S1U1P14S1S1P0 turns. The current in the solenoid changes at a rate of 6.0 A/s. A conducting loop of radius 0.0200 m is placed at the center of the solenoid with its axis the same as that of the solenoid as shown.  
-Determine the mutual inductance of this combination.

Accepted Answer

A) 1.8 × 10-4 H 
B) 2.4 × 10-4 H 
C) 3.6 × 10-4 H 
D) 4.4 × 10-4 H 
E) 5.9 × 10-4 H 
A) 1.8 × 10-4 H 
B) 2.4 × 10-4 H 
C) 3.6 × 10-4 H 
D) 4.4 × 10-4 H 
E) 5.9 × 10-4 H

Question 4

Two coils, 1 and 2, with iron cores are positioned as shown in the figure. Coil 1 is part of a circuit with a battery and a switch.  
-Assume S has been closed for a long time. Which one of the following statements is true when coil 1 and its core are moved toward point B?

Accepted Answer

A) There is no induced current in r. 
B) There is a magnetic field in coil 1 that points toward B. 
C) There is an induced current in R that flows from left to right. 
D) There is an induced current in R that flows from right to left. 
E) There is an induced magnetic field in coil 2 that points toward B. 
A) There is no induced current in r. 
B) There is a magnetic field in coil 1 that points toward B. 
C) There is an induced current in R that flows from left to right. 
D) There is an induced current in R that flows from right to left. 
E) There is an induced magnetic field in coil 2 that points toward B.

Question 5

The Earth's magnetic field passes through a square tabletop with a magnitude of 4.95 × 10-5 T and is directed at an angle of 165° relative to the normal of the tabletop. If the tabletop has 1.50-m sides, what is the magnitude of the magnetic flux through it?

Accepted Answer

A) 1.08 × 10-4 Wb 
B) 7.11 × 10-5 Wb 
C) 2.88 × 10-5 Wb 
D) 1.92 × 10-5 Wb 
E) 3.30 × 10-6 Wb 
A) 1.08 × 10-4 Wb 
B) 7.11 × 10-5 Wb 
C) 2.88 × 10-5 Wb 
D) 1.92 × 10-5 Wb 
E) 3.30 × 10-6 Wb

Question 6

The angular speed of a motor is 262 rad/s. The back emf generated by the motor is 89.4 V. Assuming all other factors remain the same, determine the back emf if the angular speed of the motor is reduced to 131 rad/s.

Accepted Answer

A) 32.3 V 
B) 44.7 V 
C) 52.5 V 
D) 89.4 V 
E) 152 V 
A) 32.3 V 
B) 44.7 V 
C) 52.5 V 
D) 89.4 V 
E) 152 V

Question 7

A small power plant produces a voltage of 6.0 kV and 150 A. The voltage is stepped up to 240 kV by a transformer before it is transmitted to a substation. The resistance of the transmission line between the power plant and the substation is 75 $\varOmega$.
-What percentage of the power produced at the power plant is lost in transmission to the substation?

Accepted Answer

A) 0.47 % 
B) 0.41 % 
C) 0.34 % 
D) 0.23 % 
E) 0.12 % 
A) 0.47 % 
B) 0.41 % 
C) 0.34 % 
D) 0.23 % 
E) 0.12 %

Question 8

Two conducting loops carry equal currents I in the same direction as shown in the figure. If the current in the upper loop suddenly drops to zero, what will happen to the current in the lower loop according to Lenz's law?

Accepted Answer

A) The current in the lower loop will decrease. 
B) The current in the lower loop will increase. 
C) The current in the lower loop will not change. 
D) The current in the lower loop will also drop to zero. 
E) The current in the lower loop will reverse its direction. 
A) The current in the lower loop will decrease. 
B) The current in the lower loop will increase. 
C) The current in the lower loop will not change. 
D) The current in the lower loop will also drop to zero. 
E) The current in the lower loop will reverse its direction.

Question 9

Which one of the following statements concerning transformers is false?

Accepted Answer

A) Their operation makes use of mutual induction. 
B) They are an application of Faraday's and Lenz's laws. 
C) A transformer can function with either an ac current or a steady dc current. 
D) A transformer that steps down the voltage, steps up the current. 
E) A transformer that steps up the voltage, steps down the current. 
A) Their operation makes use of mutual induction. 
B) They are an application of Faraday's and Lenz's laws. 
C) A transformer can function with either an ac current or a steady dc current. 
D) A transformer that steps down the voltage, steps up the current. 
E) A transformer that steps up the voltage, steps down the current.

Question 10

A solenoid with 1000 turns has a cross-sectional area of 7.0 cm2 and length of 25 cm. How much energy is stored in the magnetic field of the solenoid when it carries a current of 10.0 A?

Accepted Answer

A) 0.10 J 
B) 2.8 J 
C) 0.18 J 
D) 28 J 
E) 0.36 J 
A) 0.10 J 
B) 2.8 J 
C) 0.18 J 
D) 28 J 
E) 0.36 J

Question 11

A loop with a resistance of 4.0 $\varOmega$ is pushed to the left at a constant speed of 2.0 m/s by a 24 N force. At the instant shown in the figure, the loop is partially in and partially out of a uniform magnetic field. An induced current flows from left to right through the resistor. The length and width of the loop are 2.0 m and 1.0 m, respectively.  
-Determine the magnitude of the uniform magnetic field.

Accepted Answer

A) 2.2 T 
B) 3.5 T 
C) 6.4 T 
D) 7.0 T 
E) 9.1 T 
A) 2.2 T 
B) 3.5 T 
C) 6.4 T 
D) 7.0 T 
E) 9.1 T

Question 12

Two coils, 1 and 2, with iron cores are positioned as shown in the figure. Coil 1 is part of a circuit with a battery and a switch.  
-Assume that S has been closed for a long time. Which one of the following changes will result in an induced magnetic field in coil 2 that points toward C?

Accepted Answer

A) The switch S is opened. 
B) The iron core is removed from coil 1. 
C) Coil 1 and its core are moved toward A. 
D) Coil 1 and its core are moved toward B. 
E) Coil 2 and its core are moved toward C. 
A) The switch S is opened. 
B) The iron core is removed from coil 1. 
C) Coil 1 and its core are moved toward A. 
D) Coil 1 and its core are moved toward B. 
E) Coil 2 and its core are moved toward C.

Question 13

The figure shows a uniform magnetic field that is normal to the plane of a conducting loop with resistance R. Which one of the following changes will cause an induced current to flow through the resistor?

Accepted Answer

A) decreasing the area of the loop 
B) decreasing the magnitude of the magnetic field 
C) increasing the magnitude of the magnetic field 
D) rotating the loop through 90° about an axis in the plane of the paper 
E) all of the above 
A) decreasing the area of the loop 
B) decreasing the magnitude of the magnetic field 
C) increasing the magnitude of the magnetic field 
D) rotating the loop through 90° about an axis in the plane of the paper 
E) all of the above

Question 14

A loop with a resistance of 4.0 $\varOmega$ is pushed to the left at a constant speed of 2.0 m/s by a 24 N force. At the instant shown in the figure, the loop is partially in and partially out of a uniform magnetic field. An induced current flows from left to right through the resistor. The length and width of the loop are 2.0 m and 1.0 m, respectively.  
-Determine the magnitude of the induced current through the resistor.

Accepted Answer

A) 2.0 A 
B) 3.5 A 
C) 4.6 A 
D) 7.2 A 
E) 11 A 
A) 2.0 A 
B) 3.5 A 
C) 4.6 A 
D) 7.2 A 
E) 11 A

Question 15

A 1.2-kg rod that has a length of 1.0 m and a resistance of 5.0 $\varOmega$ slides with constant speed down a pair of frictionless vertical conducting rails that are joined at the bottom. Other than the rod, the rest of the circuit is resistanceless. A uniform magnetic field of magnitude 3.0 T is perpendicular to the plane formed by the rod and the rails as shown. Determine the speed of the rod.

Accepted Answer

A) 0.38 m/s 
B) 0.90 m/s 
C) 2.6 m/s 
D) 6.5 m/s 
E) 8.7 m/s 
A) 0.38 m/s 
B) 0.90 m/s 
C) 2.6 m/s 
D) 6.5 m/s 
E) 8.7 m/s

Question 16

The figure shows a uniform magnetic field that is normal to the plane of the conducting loop of resistance R. Note: the area of the non-circular portion of the circuit is negligible compared to that of the loop.  
-A circular loop of copper wire with an area of 2.0 m2 lies in a plane perpendicular to a time-dependent magnetic field oriented as shown. The time-dependence of the field is shown in the graph.   Which one of the entries in the table below is incorrect?

Accepted Answer

A)    
B)    
C)    
D)    
E)    
A)    
B)    
C)    
D)    
E)

Question 17

Two coils, 1 and 2, with iron cores are positioned as shown in the figure. Coil 1 is part of a circuit with a battery and a switch.  
-Assume that S has been closed for a long time. Which one of the following statements is true if S is suddenly opened?

Accepted Answer

A) There is no induced current through R. 
B) There is no induced magnetic field in coil 2. 
C) There is an induced current in R that flows from right to left. 
D) There is an induced magnetic field in coil 2 that points toward C. 
E) There is an induced magnetic field in coil 2 that points toward B. 
A) There is no induced current through R. 
B) There is no induced magnetic field in coil 2. 
C) There is an induced current in R that flows from right to left. 
D) There is an induced magnetic field in coil 2 that points toward C. 
E) There is an induced magnetic field in coil 2 that points toward B.

Question 18

A 0.100-m long solenoid has a radius of 0.050 m and 1.50 × 10S1U1P14S1S1P0 turns. The current in the solenoid changes at a rate of 6.0 A/s. A conducting loop of radius 0.0200 m is placed at the center of the solenoid with its axis the same as that of the solenoid as shown.  
-Determine the induced emf in the loop if the loop is oriented so that its axis is perpendicular to the axis of the solenoid, instead of parallel.

Accepted Answer

A) 0.7 × 10-4 V 
B) 1.4 × 10-4 V 
C) 2.8 × 10-4 V 
D) 5.6 × 10-4 V 
E) zero volts 
A) 0.7 × 10-4 V 
B) 1.4 × 10-4 V 
C) 2.8 × 10-4 V 
D) 5.6 × 10-4 V 
E) zero volts

Question 19

A flexible, circular conducting loop of radius 0.15 m and resistance 4.0 $\varOmega$ lies in a uniform magnetic field of 0.25 T. The loop is pulled on opposite sides by equal forces and stretched until its enclosed area is essentially zero mS1U1P12S1S1P0, as suggested in the drawings. It takes 0.30 s to close the loop.  
-At what rate is heat generated in the loop?

Accepted Answer

A) 3.6 × 10-3 W 
B) 8.7 × 10-4 W 
C) 8.7 × 104 W 
D) 8.1 × 105 W 
E) 8.1 × 10-5 W 
A) 3.6 × 10-3 W 
B) 8.7 × 10-4 W 
C) 8.7 × 104 W 
D) 8.1 × 105 W 
E) 8.1 × 10-5 W

Question 20

A circular coil of wire has 25 turns and has a radius of 0.075 m. The coil is located in a variable magnetic field whose behavior is shown on the graph. At all times, the magnetic field is directed at an angle of 75° relative to the normal to the plane of a loop. What is the average emf induced in the coil in the time interval from t = 5.00 s to 7.50 s?

Accepted Answer

A) -18 mV 
B) -49 mV 
C) -92 mV 
D) -140 mV 
E) -180 mV 
A) -18 mV 
B) -49 mV 
C) -92 mV 
D) -140 mV 
E) -180 mV

Exam 22: Electromagnetic Induction

A transformer changes 120 V across the primary to 1200 V across the secondary. If the secondary coil has 800 turns, how many turns does the primary coil have?

Two coils, 1 and 2, with iron cores are positioned as shown in the figure. Coil 1 is part of a circuit with a battery and a switch. -Assume S has been closed for a long time. Which one of the following statements is true when coil 1 and its core are moved toward point B?

The Earth's magnetic field passes through a square tabletop with a magnitude of 4.95 × 10-5 T and is directed at an angle of 165° relative to the normal of the tabletop. If the tabletop has 1.50-m sides, what is the magnitude of the magnetic flux through it?

The angular speed of a motor is 262 rad/s. The back emf generated by the motor is 89.4 V. Assuming all other factors remain the same, determine the back emf if the angular speed of the motor is reduced to 131 rad/s.

Two conducting loops carry equal currents I in the same direction as shown in the figure. If the current in the upper loop suddenly drops to zero, what will happen to the current in the lower loop according to Lenz's law?

Which one of the following statements concerning transformers is false?

A solenoid with 1000 turns has a cross-sectional area of 7.0 cm2 and length of 25 cm. How much energy is stored in the magnetic field of the solenoid when it carries a current of 10.0 A?

Two coils, 1 and 2, with iron cores are positioned as shown in the figure. Coil 1 is part of a circuit with a battery and a switch. -Assume that S has been closed for a long time. Which one of the following changes will result in an induced magnetic field in coil 2 that points toward C?

The figure shows a uniform magnetic field that is normal to the plane of a conducting loop with resistance R. Which one of the following changes will cause an induced current to flow through the resistor?

Two coils, 1 and 2, with iron cores are positioned as shown in the figure. Coil 1 is part of a circuit with a battery and a switch. -Assume that S has been closed for a long time. Which one of the following statements is true if S is suddenly opened?

Introduction and Mathematical Concepts

Kinematics in One Dimension

Kinematics in Two Dimensions

Forces and Newtons Laws of Motion

Dynamics of Uniform Circular Motion

Work and Energy

Impulse and Momentum

Rotational Kinematics

Rotational Dynamics

Simple Harmonic Motion and Elasticity

Fluids

Temperature and Heat

The Transfer of Heat

The Ideal Gas Law and Kinetic Theory

Thermodynamics

Waves and Sound

The Principle of Linear Superposition and Interference Phenomena

Electric Forces and Electric Fields

Electric Potential Energy and the Electric Potential

Electric Circuits

Magnetic Forces and Magnetic Fields

Alternating Current Circuits

Electromagnetic Waves

The Refl Ection of Light: Mirrors

The Refraction of Light: Lenses and Optical Instruments

Interference and the Wave Nature of Light

Special Relativity

Particles and Waves

The Nature of the Atom

Nuclear Physics and Radioactivity

Ionizing Radiation, Nuclear Energy, and Elementary Particles

Filters

The Earth's magnetic field passes through a square tabletop with a magnitude of 4.95 × 10^-⁵ T and is directed at an angle of 165° relative to the normal of the tabletop. If the tabletop has 1.50-m sides, what is the magnitude of the magnetic flux through it?

A solenoid with 1000 turns has a cross-sectional area of 7.0 cm² and length of 25 cm. How much energy is stored in the magnetic field of the solenoid when it carries a current of 10.0 A?