A particle of mass $m$ and charge $q$ describes a circular path of radius $R$ in a magnetic field. If its mass and charge were $2 m$ and $\frac{q}{2}$ respectively, the radius of its path would be

Which of the following pairs is that of paramagnetic materials?

A galvanometer of resistance $50 \Omega$ is converted into a voltmeter of range $(0-2 \mathrm{~V})$ using a resistor of $1.0 \mathrm{k} \Omega$. If it is to be converted into a voltmeter of range ( $0-10 \mathrm{~V}$ ), the resistance required will be

Two coils are placed near each other. When the current in one coil is changed at the rate of $5 \mathrm{~A} / \mathrm{s}$, an emf of 2 mV is induced in the other. The mutual inductance of the two coils is