When more than two inductors of different inductances are connected in parallel in a circuit, the total inductance

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

Answer: (A)

When inductors are connected in parallel, the same voltage is across each one, and the currents sum. Because the inductors share current in a way that reduces the overall opposition to a changing current, the equivalent inductance becomes smaller than any single coil in the group. For two inductors, L_eq = (L1*L2)/(L1+L2), which is less than both L1 and L2. With more inductors, 1/L_eq = sum(1/L_i), so L_eq is smaller than the smallest individual inductance among them. Therefore the total inductance is less than the inductance of the lowest rated inductor. For example, 4 μH and 6 μH in parallel give 2.4 μH, which is indeed less than 4 μH.