Energy in an inductor: As the current in an inductor decreases, what happens to the energy stored in its magnetic field?

Introduction / Context:
Inductors store energy in a magnetic field proportional to the square of current. Understanding how energy changes with current is essential for analyzing transients, flyback behavior, and energy transfer in converters.

Given Data / Assumptions:

• Inductor with inductance L, carrying current I.
• Current is decreasing in magnitude.
• No exotic effects (e.g., core hysteresis) are considered.

Concept / Approach:

The stored energy is W = (1/2) * L * I^2. Because I^2 is the determining factor, any decrease in |I| reduces W. If I tends to zero, energy tends to zero; the inductor releases energy back into the circuit.

Step-by-Step Solution:

Verification / Alternative check:

Consider an RL decay: i(t) = I0 * e^(−t/τ). Then W(t) = 0.5 * L * I0^2 * e^(−2t/τ), clearly decreasing over time.

Why Other Options Are Wrong:

'Increases' contradicts the I^2 dependence. 'Remains the same' would require constant current. 'Doubles' would need current magnitude to increase by √2.

Common Pitfalls:

Confusing stored energy with instantaneous voltage across the inductor; energy depends on current, not directly on voltage.

Final Answer:

decreases