Electromagnetic induction
1.
In each of the following situations, a bar magnet is aligned along the axis of a conducting loop. The magnet
and the loop move with the indicated velocities. In which situation will the bar magnet NOT induce a current
in the conducting loop?
Questions 2-3
2.
A loop of wire is pulled with constant velocity v to the right through a region of space where there is a uniform
magnetic field B directed into the page, as shown above. The magnetic force on the loop is
(A) directed to the left both as it enters and as it leaves the region
(B) directed to the right both as it enters and as it leaves the region
(C) directed to the left as it enters the region and to the right as it leaves
(D) directed to the right as it enters the region and to the left as it leaves
(E) zero at all times
3.
Which of the following represents the direction of the induced current in the loop as it enters and as it leaves
the region?
(A) zero both times
Clockwise
(B) Clockwise, zero
(E) zero, Counter Clockwise
(C) Counter clockwise, Clockwise
(D) Clockwise, Counter
Questions 4-5
A square loop of wire of side 0.5 meter and resistance 10-2 ohm is located in a uniform magnetic field of
intensity 0.4 T directed out of the page as shown above. The magnitude of the field is decreased to zero at a
constant rate in 2 seconds.
4. As the field is decreased, what is the magnitude of the current in the loop?
(A) Zero
(B) 5 A
(C) 10 A
(D) 15 A
(E) 20 A
5. What direction does the induced current flow through the loop?
(A) No direction
(B) Counter clockwise
(C) Clockwise
(D) Alternates
(E) Cannot be determined
Questions 6-7 refer to the diagram below of two conducting loops having a common axis.
6.
After the switch S is closed, the current through resistor R2 is
(A) from point X to point Y
(B) from point Y to point X
(D) oscillating with decreasing amplitude
7.
(C) zero at all times
(E) oscillating with constant amplitude
After the switch S has been closed for a very long time, the currents in the two circuits are
(A) zero in both circuits
(B) zero in circuit 1 and V/R2 in circuit 2
(C) V/R1 in circuit 1 and zero in circuit 2
(D) V/R1 in circuit I and V/R2 in circuit 2
(E) oscillating with constant amplitude in both circuits
8. Two identical parallel conducting rings have a common axis and are separated by a distance a, as shown above.
The two rings each carry a current I, but in opposite directions. At point P, the center of the ring on the left the
magnetic field due to these currents is
(A) zero
(B) in the plane perpendicular to the x-axis
(D) directed in the negative x-direction
9.
(C) directed in the positive x-direction
(E) none of the above
In the figure above, the north pole of the magnet is first moved down toward the loop of wire, then
withdrawn upward. As viewed from above, the induced current in the loop is
(A) always clockwise with increasing magnitude (B) always clockwise with decreasing magnitude
(C) always counterclockwise with increasing magnitude (D) always counterclockwise with decreasing
magnitude
(E) first counterclockwise, then clockwise
10. A vertical length of copper wire moves to the right with a steady velocity v in the direction of a constant
horizontal magnetic field B as shown above. Which of the following describes the induced charges on the ends
of the wire?
Top End
(A) Positive
(B) Negative
(C) Negative
(D) Zero
(E) Zero
Bottom End
Negative
Positive
Zero
Negative
Zero
11. A square wire loop with side L and resistance R is held at rest in a uniform magnetic field of magnitude B
directed out of the page, as shown above. The field decreases with time t according to the equation B = a - bt,
where a and b are positive constants. The current I induced in the loop is
(B) aL2/R, clockwise
(A) zero
(D) bL2/R, clockwise
(C) aL2/R, counterclockwise
(E) bL2/R, counterclockwise
Questions 12-13
A square wire loop with side length l travels with speed v through a magnetic field of strength B.
12. Which of the following will not induce a current in the loop?
(A) increasing the strength of the magnetic field
(B) stretching the loop making a larger circle
(C) moving the loop parallel to the field
(D) removing the loop from field
(E) rotating the loop about a diameter
13. Which of the following represents the magnetic flux through the loop?
(B) Bl2
(A) Blv
(C) zero
(D) Bv/l2
(E) B2v
2s
d
s
14. Two concentric loops have radii s and 2s with a spatially uniform magnetic field within the region r<d with d<s
that changes at a constant rate. The voltage induced in the outer loop is V. The voltage induced in the inner loop is
(A) 0
(B) V
(C) V/2
(D) 2V
(E) 4V
15. A wire loop of area A is placed in a time varying but spatially uniform magnetic field that is perpendicular to
the plane of the loop, as shown above. The induced emf in the loop is given by  = bAt1/2, where b is a
constant. The time varying magnetic field could be given by
(A)
1
bAt 1 / 2
2
(B)
B
l
1 1 / 2
bt
2
(C)
1 1/ 2
bt
2
(D)
2
bAt 3 / 2
3
(E)
2 3/ 2
bt
3
v
16. A wire of length l is moved through a uniform magnetic field of strength B at a constant velocity perpendicular
to the magnetic field. The induced voltage E as a function of time would look like
(A)
E
(B)
t
Questions 17-18
E
(C)
t
E
(D)
t
E
(E)
E
t
t
v
i
17. A rectangular loop moves with velocity v towards a long wire carrying a current i towards the top of the page.
Which direction will the induced current in the loop flow?
(A) Clockwise
(B) Counter Clockwise
(C) Into the page (D) Out of the page
(E) No current flows
18. The force exerted by the wire on the loop is directed in which direction?
(A) Into the page (B) Out of the Page
(C) Up
(D) Right
(E) Left
L
W
L
L
19. A rectangular loop of dimensions L and W and resistance R lays stationary in an increasing magnetic field. For a
current I to be induced in the loop the field must change at a rate of
(A) IR/LW
(B) L/IRW
(C) L/IR
(D) IRW/L
(E) IR/L
20. A circular loop is placed in a decreasing magnetic field. Which direction will the current be induced?
(A) Clockwise
(B) Counter Clockwise
(C) Into the page (D) Out of the page
(E) No current flows
Questions 21-23
B
R
l
A C-shaped conductor is in a uniform magnetic field B as shown above. A metal rod of length l is placed between
the 2 sides of the conductor and forms the circuit of total resistance R. The rod moves to the right with its position
given by the function x=a2t+b.
21. Which of the following represents the direction of the induced current through the loop?
(A) Into the page (B) Out of the page(C) Clockwise
(D) Counter Clockwise
(E) None
22. Which of the following represents the direction of the magnetic force on the rod?
(A) Up
(B) Down
(C) Left
(D) Right
(E) Into the page
23. Which of the following represents the magnitude of the induced current in the loop?
(A) Bl(a2+b)/R
(B) 2Bla/R
(D) Bla2/R
(C) Bl/R
(E) Bla2/2R
24. A loop of wire is placed in a constant magnetic field B and begins to rotate about its diameter. Which of the
following represents the magnetic flux through the loop as a function of time?
(A)
(B)
(C)
(D)
(E)
Φ
Φ
t of the following
t is true?
25. Which
Φ
Φ
t
Φ
t
t
I. The induced current in the loop will oppose the change in the magnetic field
II. The induced current through a stationary loop of wire with constant magnetic field is 0
III. The induced current will create an electric field that opposes the magnetic field
(A) I only
(B) I and II only
(C) I and III only (D) All of the above
(E) None of the above
Answers
1. E
2. A
3. C
4. B
5.B
6. A
7. C
8. C
9. E
10. E
11. E
12. C
13. C
14. B
15. E
16. C
17. B
18. D
19. A
20. A
21. D
22. C
23. D
24. C
25. B