Inductance affects a DC circuit only when what occurs?

• A. The current is steady
• B. The current is changing
• C. The voltage is zero
• D. Power is constant

Answer: (B)

Inductors respond to changes in current, not to a steady current. The defining relation v = L di/dt means the voltage across an inductor appears only when the current is changing. In DC steady state, di/dt is zero, so the voltage across the inductor is zero and it behaves essentially like a short piece of wire, not affecting the current. The inductance thus matters during transient events—when you switch a circuit on or off and the current is ramping up or down. That’s when the inductor resists the change, stores energy in its magnetic field, and creates a transient response characterized by the time constant L/R. The other scenarios describe steady conditions where no di/dt occurs, so the inductance isn’t exerting an effect.