Question

The magnetic potential energy stored in a certain inductor is \(49 \text{mJ}\) when the current in the inductor is \(70 \text{mA}\). The inductance of the inductor is

• A. \(0.20 \text{H}\)
• B. \(2.0 \text{H}\)
• C. \(20 \text{H}\)
• D. \(200 \text{H}\)

Hint:

Use U = (1/2) L I squared.

Answer 1

The Correct Option is C

Step 1: Work in milli units:
$U = 49 \times 10^{-3}$ J, $I^2 = 4900 \times 10^{-6}$ A$^2$.

Step 2: Divide:
$L = \frac{98 \times 10^{-3}}{4.9 \times 10^{-3}} = 20$ H.

Final Answer:
$L = 20$ H, option (C). \[ \boxed{20\ \text{H}} \]