A metre bridge experiment, the resistance in the left gap is $20\ \Omega$ and in the right gap is $60\ \Omega$. The bridge is balanced. The distance of the null point from the centre of the wire is

The magnetic moment produced in a sample of 2 gram is $8 \times 10^{-7}\,\text{A/m}^2$. If its density is $4\ \text{g/cm}^3$ then the magnetization of the sample is

A wire carrying current 'I' along x axis has length 'L' and it is kept in a magnetic field $B(\hat{i}+2\hat{j}-2\hat{k})$ T. The magnitude of magnetic force acting on the wire is

A charged particle is moving in a uniform magnetic field in a circular path of radius 'R'. When the energy of the particle becomes 3 times the original, the new radius will be