Alternating Current - Result Question 21
21. A coil has resistance $30 ohm$ and inductive reactance $20 ohm$ at $50 Hz$ frequency. If an ac source, of 200 volt, $100 Hz$, is connected across the coil, the current in the coil will be [2011M]
(a) $4.0 A$
(b) $8.0 A$
(c) $\frac{20}{\sqrt{13}} A$
(d) $2.0 A$
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Answer:
Correct Answer: 21. (a)
Solution:
- (a) If $\omega=50 \times 2 \pi$ then $\omega L=20 \Omega$
If $\omega^{\prime}=100 \times 2 \pi$ then $\omega^{\prime} L=40 \Omega$
Current flowing in the coil is
$I=\frac{200}{Z}=\frac{200}{\sqrt{R^{2}+(\omega^{\prime} L)^{2}}}=\frac{200}{\sqrt{(30)^{2}+(40)^{2}}}$
$I=4 A$.
