magnetism Questions

A magnetic needle lying parallel to a magnetic field requires $W$ units of work to turn it through $60^{\circ }$. The torque needed to maintain the needle in this position will be:

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon:

A particle of mass $M$ and charge $Q$ moving with velocity $\vec{v}$ describes a circular path of radius $R$ when subjected to a uniform transverse magnetic field of induction $B$. The work done by the field when the particle completes one full circle is:

The magnetic lines of force inside a bar magnet:

The core of any transformer is laminated so as to:

Curie temperature is the temperature above which:

A thin rectangular magnet suspended freely has a period of oscillation equal to $T$. Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely in the same field. If its period of oscillation is $T^{\prime }$, the ratio $T^{\prime }/T$ is:

When the current changes from $+2\text{A}$ to $-2\text{A}$ in $0.05$ second, an e.m.f. of $8\text{V}$ is induced in a coil. The coefficient of self-induction of the coil is: