When inductors are connected in series in a circuit, the total inductance is (LT = L1 + L2 + L3 ...)?

• A. equal to the sum of the individual inductances.
• B. less than the inductance of the lowest rated inductor.
• C. equal to the inductance of the highest rated inductor.
• D. greater than the sum of the inductances

Answer: (A)

When inductors are connected in series, the same current flows through each one, and the induced voltage across an inductor follows v = L di/dt. The total voltage across the series chain is the sum of the individual voltages: v_total = v1 + v2 + v3 = L1 di/dt + L2 di/dt + L3 di/dt = (L1 + L2 + L3) di/dt. Since the chain behaves as a single inductor with v_total = L_total di/dt, the total inductance must equal the sum of the individual inductances: L_total = L1 + L2 + L3, and so on. This is why the total inductance in series is simply the sum. If you double two equal inductors in series, you double the inductance; in parallel, the situation changes and the reciprocals add.