In the circuit of measuring inductance by RLC series resonance method, the voltmeter is connected to the capacitor, the inductor and the main circuit respectively, and their readings do not conform to the simple U=U 1+U2. If the vector is calculated in the formula, it is.

Because in alternating current, the voltage of inductor leads the current, and the current of capacitor leads the voltage. Therefore, their voltage relationship is a vector relationship, which should be solved by trigonometry or graphic method.