Two inductors with inductances of 4 millihenries and 3 millihenries are connected in series. What is the total inductance?

• A. 7 millihenries
• B. 12 millihenries
• C. 1 millihenry
• D. 3 millihenries

Answer: (A)

When inductors are placed in series, the same current flows through both resistors, and their inductances add together to form a single equivalent inductance. This happens because the total voltage across the series pair is the sum of the voltages across each inductor: v = L1 di/dt + L2 di/dt = (L1 + L2) di/dt. So the effective inductance of the series combination is L1 + L2.

Here, L1 is 4 millihenries and L2 is 3 millihenries, so the total inductance is 4 mH + 3 mH = 7 mH. That’s why 7 millihenries is the correct total.

The other numbers would stem from different configurations or misunderstandings: for example, 1 mH would imply taking only one coil or subtracting, and 3 mH would be just one of the inductances by itself, not the combined series value.