In an electrical circuit two resistors of $2\,\Omega $ and $4\,\Omega $ respectively are connected in series to a $6\, V$ battery. The heat dissipated by the $4\,\Omega $ resistor in $5\, s$ will be ........ $J$

$(a)$ In the circuit shown connect a nichrome wire of length ${ }^{\prime \prime} L^{\prime \prime}$ between points $X$ and $Y$ and note the ammeter reading.

$(i)$ When this experiment is repeated by inserting another nichrome wire of the same thickness but twice the length $(2 L),$ what changes are observed in the ammeter reading ?

$(ii)$ State the changes that are observed in the ammeter reading if we double the area of cross-section without changing the length in the above experiment. Justify your answer in both the cases.

$(b)$ "Potential difference between points $A$ and $B$ in an electric field is $1\, V^{\prime \prime} .$ Explain the statement.

When is potential difference between two points said to be $1$ volt ?

A potential difference $V$ is applied across a conductor of length $L$ and diameter $D .$ How is the resistance $R$ of the conductor affected, when in turn $(i)$ $V$ is halved $(ii)$ $L$ is halved and $(iii)$ $D$ is doubled ? Justify your answer in each case.

In a circuit containing two unequal resistors connected in parallel

A bulb gets dimmer for a moment when a geyser, connected across the same source is switched on. Why ?