A bar of iron having magnetic moment $2.4 \mathrm{Am}^2$ weighs 66 g . If the density of the material of the bar is $7700 \mathrm{~kg} / \mathrm{m}^3$, the intensity of magnetisation in $\mathrm{Am}^{-1}$ is

The error in the measurement of length and mass is $3 \%$ and $4 \%$ respectively. The error in the measurement of density will be

The potentiometer wire is 5 m long and potential difference of 4 V is maintained between the ends. The e.m.f. of the cell which balances against a length of 200 cm of the potentiometer wire is

Moment of inertia of the rod about an axis passing through the centre and perpendicular to its length is ' $I_1$ '. The same rod is bent into a ring and its moment of inertia about the diameter is ' $I_2$ '. Then $I_1 / I_2$ is