Electro Magnetic Induction And Alternating Currents Question 129
Question: When 100 volts dc is supplied across a solenoid, a current of 1.0 amperes flows in it. When 100 volts ac is applied across the same coil, the current drops to 0.5 ampere. If the frequency of ac source is 50 Hz, then the impedance and inductance of the solenoid are [CPMT 1990]
Options:
A) 200 W and 0.55 henry
B) 100 W and 0.86 henry
C) 200 W and 1.0 henry
D) 100 W and 0.93 henry
Show Answer
Answer:
Correct Answer: A
Solution:
For dc, $ R=\frac{V}{i}=\frac{100}{1}=100\Omega $
For ac, $ Z=\frac{V}{i}=\frac{100}{0.5}=200\Omega $
$ \because ,Z=\sqrt{R^{2}+{{(\omega L)}^{2}}} $
Þ $ 200=\sqrt{{{(100)}^{2}}+4{{\pi }^{2}}{{(50)}^{2}}L^{2}} $ \ $ L=0.55H $
