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Induction and Lenz’s Law Review- 2014
Name________________________
AP Physics 2
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1. A conducting loop of wire is placed in a magnetic field that is normal to the plane of the loop.
Which one of the following actions will not result in an induced current in the loop?
*A) Rotate the loop about an axis that is parallel to the field and passes through the center of the
loop.
B) Increase the strength of the magnetic field.
C) Decrease the area of the loop.
D) Decrease the strength of the magnetic field.
E) Rotate the loop about an axis that is perpendicular to the field and passes through the center
of the loop.
2. 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 1.50m sides, what is the magnitude of the magnetic flux through it?
*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
3. A circular copper loop is placed perpendicular to a uniform magnetic field of 0.75 T. Due to
external forces, the area of the loop decreases at a rate of 7.26 × 10–3 m2/s. Determine the
induced emf in the loop.
A) 3.1 × 10–4 V
B) 6.3 × 10–4 V
C) 1.2 × 10–3 V
*D) 5.4 × 10–3 V
E) 3.1 V
4. A 250-turn solenoid carries a current of 9.0 A. The radius of the solenoid is 0.075 m; and its
length is 0.14 m. Determine the magnetic flux through the circular cross-sectional area at the
center of the solenoid.
A) 1.8 × 10–5 Wb
B) 9.9 × 10–5 Wb
*C) 3.6 × 10–4 Wb
D) 7.0 × 10–4 Wb
E) 2.2 × 10–3 Wb
5. The figure below shows a uniform, 3.0-T magnetic field that is normal to the plane of a
conducting, circular loop with a resistance of 1.5  and a radius of 0.024 m. The magnetic field
is directed out of the paper as shown. Note: The area of the non-circular portion of the wire is
considered negligible compared to that of the circular loop.
What is the magnitude of the average induced emf in the loop if the magnitude of the magnetic
field is doubled in 0.4 s?
A) 0.43 V
B) 0.65 V
*C) 0.014 V
D) 0.027 V
E) 0.038 V
6. What is the average current around the loop if the magnitude of the magnetic field is doubled
in 0.4 s?
A) 2.8 × 10–3 A, clockwise
B) 4.5 × 10–3 A, clockwise
C) 4.5 × 10–3 A, counterclockwise
*D) 9.0 × 10–3 A, clockwise
E) 9.0 × 10–3 A, counterclockwise
7. A long, straight wire is in the same plane as a rectangular, conducting loop. The wire carries
a constant current I as shown in the figure. Which one of the following statements is true if the
wire is suddenly moved toward the loop?
A) There will be no induced emf and no induced current.
B) There will be an induced emf, but no induced current.
C) There will be an induced current that is clockwise around the loop.
*D) There will be an induced current that is counterclockwise around the loop.
E) There will be an induced electric field that is clockwise around the loop.
8. Which of the following units are equivalent to those of motional emf?
A) T  m/s
E) T * m
2
B) V  m /s
C) J/s
*D) A  
9.. Which one of the following statements concerning transformers is false?
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.
10. A circular loop of copper wire with an area of 2.0 m2 lies in a plane perpendicular to a timedependent 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?
Time
Induced emf
A)
1s
zero volts
4s
2.5 V, counterclockwise
5s
2.5 V, counterclockwise
7s
10 V, clockwise
9s
10 V, counterclockwise
B)
C)
D)
*E)
11. A loop with a resistance of 4.0  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.
What is the direction of the magnetic field?
A) to the left
B) to the right
C) out of the paper
*D) into the paper
E) toward the top of the page
12. A magnetic field is directed perpendicular to the plane of a 0.15-m × 0.30-m rectangular coil
consisting of 240 loops of wire. To induce an average emf of –2.5 V in the coil, the magnetic
field is increased from 0.1 T to 1.8 T during a time interval t. Determine t.
A) 0.053 s
B) 0.13 s
C) 12 s
D) 6.4 s
*E) 7.3 s