Inductor dynamics — which quantity in an ideal inductor cannot change instantaneously at the exact moment a switching event occurs?

Introduction / Context:
Inductors store energy in magnetic fields. Their fundamental behavior is governed by v = L * di/dt. This directly constrains how rapidly current through an inductor can change, which is crucial in switching converters, motor drives, and transient analysis. The question asks which quantity cannot exhibit an instantaneous jump in an ideal inductor.

Given Data / Assumptions:

• Ideal inductor with inductance L, no series resistance.
• Possibility of step changes in applied voltage (switching).
• We consider the instantaneous behavior at t = 0+ when a switch toggles.

Concept / Approach:
From v = L * di/dt, the derivative of current is finite for finite voltage. An instantaneous jump in current would require infinite di/dt, which in turn would require infinite voltage — impossible in real circuits and not permitted in idealized linear models. Therefore, in an inductor, current is continuous. Voltage, however, can change abruptly as circuit conditions change because it is proportional to the rate of change of current, not to the current itself.

Step-by-Step Solution:

Verification / Alternative check:
Observe RL step response: i(t) = I_final * (1 − exp(−t/τ)) + i(0) * exp(−t/τ) with τ = L/R. At t = 0+, the exponential term assures continuity of current, matching lab waveforms.

Why Other Options Are Wrong:

• Voltage: It can jump depending on circuit constraints, especially in series with switches or when di/dt changes sign.
• Instantaneous power: p(t) = v(t) * i(t) can change abruptly since v may step.
• Magnetic field orientation: Orientation is determined by current direction; while direction can reverse over time, the instantaneous change would again imply a current discontinuity — the governing restriction is on current.

Common Pitfalls:
Confusing capacitor and inductor continuity laws (capacitor voltage is continuous; inductor current is continuous). Mixing energy storage variables leads to wrong transient predictions.

Final Answer:
current cannot change instantaneously in an inductor.