Define $1$ volt.

How many electrons constitute a total charge of $1 \ C$?

Name the commercial unit of electrical energy. Convert it into joule. What is the other name of the commercial unit?

$(a)$ Name an instrument that measures electric current in a circuit. Define the unit of electric current.
$(b)$ What do the following symbols mean in an electric circuit?
$(c)$ Draw a closed circuit diagram consisting of a $0.5\, m$ long nichrome wire $XY$,an ammeter,a voltmeter,four cells of $1.5\, V$ each,and a plug key.

Two wires $A$ and $B$ are of the same metal,have the same area of cross-section,and have their lengths in the ratio $2:1$. What will be the ratio of currents flowing through them respectively,when the same potential difference is applied across each of them?

Should the resistance of an ammeter be low or high? Give reason.