An electric bulb works on the heating effect of current.

If $R_{1}$ and $R_{2}$ are the resistances of filaments of a $400 \ W$ and a $200 \ W$ lamp,designed to operate on the same voltage,then

$B_1, B_2$ and $B_3$ are three identical bulbs connected as shown in the figure. When all three bulbs glow,a current of $3\,A$ is recorded by the ammeter $A$.
$(i)$ What happens to the glow of the other two bulbs when the bulb $B_1$ gets fused?
$(ii)$ What happens to the reading of $A_1, A_2, A_3$ and $A$ when the bulb $B_2$ gets fused?
$(iii)$ How much power is dissipated in the circuit when all three bulbs glow together?

What is the main principle involved in a Voltaic cell?

The unit $Volt \times Ampere$ represents which physical quantity?

$(a)$ Define potential difference between two points in a conductor.
$(b)$ Name the instrument used to measure the potential difference in a circuit. How is it connected?
$(c)$ $A$ current of $2 \, A$ passes through a circuit for $1$ minute. If the potential difference between the terminals of the circuit is $3 \, V$, what is the work done in transferring the charges?