Current without EMF in AC capacitance circuit In AC circuit with only capacitance, current in circuit is maximum at time t=0 but emf of source is E=0 at t=0 , how can this happen,
How can current flows without emf. 
 A: 
How can current flows without emf.

A capacitor is not a resistor and so Ohm's law does not apply.  For a resistor, a current through implies a voltage across.  For a capacitor, a current through implies a changing voltage across.
For a sinusoidal voltage across, the rate of change is greatest when the voltage across is zero thus the current through is maximum then. 
A: Let’s break your question down into two parts. The first part:
In AC circuit with only capacitance, current in circuit is maximum at time t=0 but emf of source is E=0 at t=0 , how can this happen? 
See the circuit diagrams below for an ac source with only capacitance and ideal (zero resistance) wires. 
The first thing to understand is why current to the capacitor is a maximum at time $t=0$ when the voltage across it $V_{C}=0$. It stems from the definition of capacitance, $C$, which is the amount of charge stored on the capacitor plates per volt across the plates, or
$$C=\frac{Q}{V}$$ 
$$Q=CV$$
Electric Current, $I(t)$, through a surface is defined as the rate of charge transport through that surface, or
$$I(t)=\frac{dQ}{dt}$$
Applied to the capacitor where its capacitance C is a constant, it gives us
$$I(t)=C\frac{dV}{dt}$$
Now, if the ac voltage source, $V$, is a sine wave, the derivative of the sine is the cosine. The cosine is 90 degrees out of phase with the sine. This means when the voltage across the capacitor is maximum (capacitor is fully charged), the current is zero, and vice versa. This is reflected in the diagrams below.
Note that if V= constant (e.g., if the source were a battery), then I=0 under steady state conditions. This reflects the fact that a capacitor has a gap between its plates. Since there is no conductive connection between the plates, electrons do not travel from one plate to another. When current is flowing in the circuit, it simply reflects the fact that electrons are flowing to and from the plates, charging and discharging the capacitor, and not across the plates. This can only happen when the capacitor is charging and discharging, i.e., when the voltage is changing in time.
Now, for the second part:
How can current flow without emf?
Current can flow without an emf because a circuit consisting of an ideal voltage source, ideal capacitor, and ideal connecting wires has no resistance to current flow. Of course, a real circuit will have resistance and therefore voltage drops across the resistance and power dissipated in resistance if current is flowing.
For the idealized circuit, energy is simply exchanged between the voltage source and the capacitor. When the voltage across the capacitor is the peak voltage $V_{P}$ of the voltage source, the energy $E$ stored in the electric field of the capacitor is given by
$$E=\frac{CV_{P}^2}{2}$$
When current flows out of the capacitor to the source, this energy is transferred back to the source.
Hope this helps.

