Why should circuits containing capacitor be handled cautiously, even when there is no current?

An alternating voltage E=E_0 sin omegat is applied to a circuit containing a resistor R connected in series with a black box. The current in the circuit is found to be I = I_0 sin(omegat+pi/4) . State whether the element in the black box is a capacitor or indutor.

Finda phase relation between current and voltage in an a.c. circuit containing a pure capacitance. A pure capacitor blocks directcurrent, why ?

Explain why the capacitance of capacitor increases when dielectri slab is inserted between the plates of the capacitor. Derive an expression for energy stored in a charged capacitor.

In an oscillating LC circuit, the maximum charge on capacitor is Q. The charge on capacitor when the energy is equally distributed between the electric and magnetic fields is