Question

Consider the LC circuit shown in (Figure 1). Suppose that vC is potential difference across the capacitor's plates, qC is charge on the capacitor, B is magnetic field in the inductor, UE is electric potential energy stored in the capacitor, and UB is magnetic potential energy stored in the inductor. Which of these quantities simultaneously reach their maximum values: |vC|, |qC|, |i|, |B|, |UE|, |UB|?

Figure 1: http://oi66.tinypic.com/2lv017t.jpg

Answer 1

As capacitor has the potential V_C at t= 0 .
Now capacitor will start to discharge and current will increase in the inductor.
Since the magnetic field in the inductor is directly proportional to the current therefore magnetic
field will also increased to the maximum simultaneously.
As per energy is concerned in the inductor it will also stored till the current is increasing in the inductor.
Hence we can say that
i ,B and U_B will reach to the maximum simultaneously.
Now when the potential across the inductor will reach equal to the capacitor then the direction of the current will
get reverse or current will start decreasing. In other word now inductor will start to charge the capacitor.
Therfore the charge will build up in the capacitor.
Therefore the q , V and U_E in the capacitor will reach to the maximum simultaneoulsy.