Question

The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. This inductor is of inductance

• A. 0.138H
• B. 1.389H
• C. 138.88H
• D. 13.89H

Answer 1

The Correct Option is D

To find the inductance, we use the formula for energy stored in an inductor:

\[ U = \frac{1}{2} L I^2 \]

Given:

• \( U = 25\,\text{mJ} = 25 \times 10^{-3}\,\text{J} \)
• \( I = 60\,\text{mA} = 60 \times 10^{-3}\,\text{A} \)

Substitution:

\[ 25 \times 10^{-3} = \frac{1}{2} L (60 \times 10^{-3})^2 \]

\[ 25 \times 10^{-3} = \frac{1}{2} L \times 3600 \times 10^{-6} \]

\[ 25 \times 10^{-3} = \frac{1}{2} L \times 3.6 \times 10^{-3} \]

\[ 50 \times 10^{-3} = L \times 3.6 \times 10^{-3} \]

\[ L = \frac{50 \times 10^{-3}}{3.6 \times 10^{-3}} = \frac{50}{3.6} \approx 13.89\,\text{H} \]

Final Answer: \( 13.89\,\text{H} \)