Question

The frequency of oscillation of the LC circuit in the figure is 200 kHz. At time t = 0 the upper capacitor plate has its maximum positive charge. Select ALL correct statements, e.g., enter AC. At t = 2.5 mu s, the charge on the lower plate has its maximum positive value. At t = 2.5 mu s, the energy is completely stored in the inductor. At t = 1.25 mu s, the charge on the lower plate has its maximum positive value. At t = 2.5 mu s, the current is zero. At t = 5.0 mu s, the current is maximum.

Answer 1

Time period of oscillations, T = 1/f
= 1/(200 x 10³)
= 5 x 10^-6 s = 5 μs

After every 5 μs, the charge on the upper capacitor plate will have maximum positive value. So, starting from zero time, after 2.5 μs, charge on the lower plate will have maximum positive value and after 5 μs, again charge on the upper plate will have maximum positive value. During 0 s, 2.5 μs, 5 μs, 7.5 μs etc., the energy is stored by the capacitor.

Initially, the capacitor is fully charged, at the very next instant, current starts to flow, and the current will be maximum. The current will decrease as the capacitor discharges and the capacitor will began to charge in the opposite direction. At 2.5 μs, the capacitor is fully charged in the opposite direction and at the next instant, maximum current will flow. So current will be maximum at 0, 2.5 μs, 5 μs etc.

The answers are A, B abd E