The area of cross-section of a potentiometer wire is $6 \times 10^{-7} \mathrm{~m}^2$. The potential difference per unit length of the potentiometer wire when it is connected to a cell of negligible internal resistance and a resistor in series is $0.15 \mathrm{Vm}^{-1}$. If the current through potentiometer wire is 0.3 A , then the resistivity of the material of the potentiometer wire is

The lengths of two wires made of the same material are in the ratio $2: 3$ and their radii are in the ratio $1: 2$. If the two wires are connected in parallel to a battery, then the ratio of the drift velocities of free electrons in the two wires is

In a potentiometer experiment for the determination of the internal resistance of a cell, when an external resistance of $R$ is connected parallel to the cell, the balancing length decreases by $10 \%$. The internal resistance of the cell is

The potential difference between the terminals of a cell is 20 V when a current of 2 A flows through the circuit. When the direction of current in the circuit is reversed, the potential difference between the terminals of the cell is 30 V . The internal resistance of the cell is