AP Physics C Electricity and Magnetism · Question of the Day

AP Physics C Electricity and Magnetism Question of the Day

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Saturday, August 22, 2026

In an ideal LC circuit, a capacitor with capacitance $C$ is initially charged to a maximum charge $Q_{max}$ . The circuit then oscillates. By conservation of energy, what is the maximum energy $U_{L,max}$ stored in the inductor during one cycle?

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$U_{L,max} = \frac{Q_{max}^2}{2C}$ (correct answer)
$U_{L,max} = \frac{1}{2} L Q_{max}^2$
$U_{L,max} = \frac{Q_{max}^2}{2L}$
$U_{L,max} = 0$

Explanation: The total energy in an ideal LC circuit is conserved. It oscillates between the capacitor's electric field and the inductor's magnetic field. The maximum energy stored in the inductor must equal the maximum energy initially stored in the capacitor, which is $U_{C,max} = \frac{Q_{max}^2}{2C}$ .