Two long conductors, separated by a distance '$$\mathrm{d}$$' carry currents '$$\mathrm{I}_1$$' and '$$\mathrm{I}_2$$' in the same directions. They exert a force '$$\mathrm{F}$$' on each other. Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to '$$3 \mathrm{~d}$$'. The new value of the force between them is

A body attached to one end of a string performs motion along a vertical circle. Its centripetal acceleration, when the string is horizontal, will be [$$\mathrm{g}=$$ acceleration due to gravity]

A coil has an area $$0.06 \mathrm{~m}^2$$ and it has 600 turns. After placing the coil in a magnetic field of strength $$5 \times 10^{-5} \mathrm{Wbm}^{-2}$$, it is rotated through $$90^{\circ}$$ in 0.2 second. The magnitude of average e.m.f induced in the coil is

$$\left[\cos 0^{\circ}=\sin 90^{\circ}=1 \text { and } \sin 0^{\circ}=\cos 90^{\circ}=0\right]$$

. If the current of '$$I$$' A gives rise to a magnetic flux '$$\phi$$' through a coil having '$$N$$' turns then mangetic energy stored in the medium surrounding the coil is