An ac source of period T and maximum voltage V is connected to a single unknown ideal element that is either a resistor, and inductor, or a capacitor. At time t = 0 the voltage is zero. At time t = T/4 the current in the unknown element is equal to zero, and at time t = T/2 the current is I = -Imax, where Imax is the current amplitude. What is the unknown element?
A) a resistor
B) an inductor
C) a capacitor
D) an inductor or a capacitor

Question

Quizplus · Accepted Answer

The current in a capacitor leads the voltage by 90 degrees (T/4 in time), so at t = T/4, the current is zero when the voltage is at its maximum. At t = T/2, the current is at its negative maximum, which matches the behavior of a capacitor.

An Ac Source of Period T and Maximum Voltage V