Inductors and Inductance – Exercise – 1

16. When the current through an inductor is cut in half, the amount of energy stored in the electromagnetic field ________.

(a) is quartered
(b) quadruples
(c) doubles
(d) does not change

Answer
Answer : (a)
Explanation
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17. The inductance of an iron-core coil decreases if ________.

(a) the number of turns is decreased
(b) the iron core is removed
(c) the length of the coil decreases
(d) none of the above

Answer
Answer : (a)
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18. Three 15 mH inductors are in series. The total inductance is ________.

(a) 15 mH
(b) 30 mH
(c) 45 mH
(d) 5 mH

Answer
Answer : (c)
Explanation
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19. A 320 μH coil is in series with a 3.3 kΩ resistor. How long does it take for current to build up to its full value?

(a) 0.48 s
(b) 0.48 ms
(c) 0.48 μs
(d) 48 s

Answer
Answer : (c)
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20. A switch, a 220 Ω resistor, and a 60 mH inductor are in series across a 20 V battery. What is the current through the inductor two time constants after the switch is closed?

(a) 91 mA
(b) 78 mA
(c) 57 mA
(d) 400 mA

Answer
Answer : (b)
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