What is phase difference between the e.m.f. and current is an a.c. circuit contains a pure capacitance?

What is the difference between e.m.f. and potential diffrence?

Phase difference between voltage and current in a.c. circuit having resistor only is:

In an a.c. circuit containing inductance

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

What is difference between ohmic resistance and impedance of an a.c. circuit.