A bar magnet is held perpendicular to a uniform field. If the couple acting on the magnet is to be halved, by rotating it, the angle by which it is to be rotated is
A negative charge particle is moving upward in a magnetic field which is towards north. The particle is deflected towards
Two point charges $$\mathrm{M}$$ and $$\mathrm{N}$$ having charges $$+q$$ and $$-q$$ respectively are placed at a distance apart. Force acting between them is $$\mathrm{F}$$. If $$30 \%$$ of charge of $$\mathrm{N}$$ is transferred to $$\mathrm{M}$$, then the force between the charges becomes:
A conducting circular loop is placed in a uniform magnetic field $$\mathrm{B}=0.125 \mathrm{~T}$$ with its plane perpendicular to the loop. If the radius of the loop is made to shrink at a constant rate of $$2 \mathrm{~mm} \mathrm{~s}^{-1}$$, then the induced emf when the radius is $$4 \mathrm{~cm}$$ is