Sensitivity of a particular potentiometer can be increased by

A $2.0 \mathrm{V}$ potentiometer is used to determine the internal resistance of a $1.5 \mathrm{V}$ cell. The balance point of the cell in open circuit is $75 \mathrm{cm}$. When a resistor of $10 \mathrm{\Omega }$ is connected across the cell, the balance point shifts to $60 \mathrm{cm}$. The internal resistance of the cell is

Assertion: We prefer a potentiometer with a longer bridge wire.

Reason: By doing this, the sensitivity of the bridge is increased because for longer wire potential drop per unit length will be small.

In the potentiometer circuit of the figure, when the key $K$ is inserted, balanced length is found to be $20 \mathrm{cm}$ for $R=10 \mathrm{\Omega }$ and $24 \mathrm{cm}$ for $R=20 \mathrm{\Omega }$. The balanced length if $\text{key}\mathit{ }K$ is taken out will be,