Inductance
1.
At time t = 0 the switch is closed in the circuit shown above. Which of the following graphs best describes the
potential difference V, across the resistance as a function of time t ?
2.
If R is 1 ohm and L is 1 henry, then L/R is
(A) 1 volt
(B) 1 farad
(C) 1 ampere
(D) 1 coulomb
(E) 1 second
Questions 3-5 relate to the following circuit in which the switch S has been open for a long time.
3.
What is the instantaneous current at point X immediately after the switch is closed?
A) 0
B) /R
C) /2R
D) /RL
E) L/2R
4. When the switch has been closed for a long time what is the energy stored in the inductor?
A) L/2R
B) L2/2R2
C) L2 /4R2
D) LR2/22
E) 2R2/4L
5. After the switch has been closed for a long time, it is opened at time t = 0. Which of the following graphs best
represents the subsequent current i at point X as a function of time t ?
(A)
(B)
(C)
(D)
(E)
Questions 6-7
A circuit consists of a battery of voltage emf E, a resistor of resistance R and an inductor of inductance L connected
in series. The current is given by the function I=(E/R)(1-
R
)t
L
6. When the circuit is first connected which of the following represents the current through the resistor R?
(A) zero
(B) E/R
(C)E/R(1- eR / L
(D) eR / L
(E/R) eR / L
7. Which of the following represents the time constant ?
(A)RL
(B) E/RL
(C)
Rt / L
(D)
R / L
(E) R/L
8. Which of the following is true about inductors?
I. They store energy over a long time
II. They resist the flow of current through it
III. They can produce a magnetic field
a
(A) I
(B) III
(C) I and II
(D) II and III
(E) all of the above
b
9. A resistor,
inductor and battery are connected in series. Which of the following represents the net voltage of the
system?
(A) iR+Ldi/dt
(B) iR-Ldi/dt
(C) Ldi/dt
(D) iR
(E) I+L+di/dt+R
Questions 10-12
The circuit above has the switch initially in position A.
10. Which of the following is true about the circuit?
(A) The current rises instantly to 7.5 A then decreases to 0
(B) The current rises instantly to 2 A then decreases to 0
(C) The current rises to 7.5 A and remains constant
(D) The current rises to 2 A and remains constant
(E) The current will remain constant after the switch closes
11. The maximum energy the inductor stores is approximately
(A) 0
(B) 8 J
(C) 16 J
(D) 60 J
(E) 110 J
12. The switch is closed to junction b after a long time. Which of the following occurs?
(A) The current drops instantly to 0
(B) The current drops uniformly to 0 over some time
(C) The current drops exponentially to 0
(D) The current oscillates with a period of 0.05s
(E) The current oscillates with a period of 0.5s
13. Which of the following can act as an inductor?
I. A long solenoid
II. A loop of wire
III. A conducting sphere
(A) I
(B) III
(C) I and II
(D) II and III
(E) all of the above
Questions 14-17 refer to the diagram below
50
a
20 V
0.1 H
b
14. What is the current in the inductor when the switch is closed into position a?
(A) zero
(B) 0.2 A
(C) 0.4 A
(D) 2 A
(E) 20 A
15. What is the current in the inductor when the switch has been closed in junction a for a long time?
(A) zero
(B) 0.2 A
(C) 0.4 A
(D) 2 A
(E) 20 A
16. What is the current in the inductor when the switch is closed to junction b?
(A) zero
(B) 0.2 A
(C) 0.4 A
(D) 2 A
(E) 20 A
17. What is the current in the inductor when the switch has been closed in junction b for a long time?
(A) zero
(B) 0.2 A
(C) 0.4 A
(D) 2 A
(E) 20 A
18. An inductor is placed in series with a capacitor to a battery. Which of the following represents the voltage of the
battery?
(A) qLdi/Cdt
(B) q/c
(C) Ldi/dt
(D) q/C-Ldi/dt (E) q/C+Ldi/dt
Questions 19-20
19. An inductor of inductance of 0.5 H is connected in series to a resistor of 5 to a 10 volt battery. Which of the
following is the time constant ?
(A) .01 s
(B) .05 s
(C) 0.1 s
(D) 2 s
(E) 25 s
20.What is the energy dissipated by this circuit?
(A) 0 J
(B) 1 J
(B) 4 J
(D) 6.25 J
(E) 25 J
Answers
1. B
2. E
3. A
4. B
5. E
6. A
7. E
8. D
9. A
10. D
11. B
12. B
13. D
14. A
15. B
16. B
17. A
18. E
19. C
20. B
