Two parallel wires in free space are $$10 \mathrm{~cm}$$ apart and each carries a current of $$10 \mathrm{~A}$$ in the same direction. The force exerted by one wire on the other [per unit length] is
A toroid with thick windings of $$N$$ turns has inner and outer radii $$R_1$$ and $$R_2$$, respectively. If it carries certain steady current $$I$$, the variation of the magnetic field due to the toroid with radial distance is correctly graphed in
A tightly wound long solenoid has $n$ turns per unit length, a radius $$r$$ and carries a current $$I$$. A particle having charge $$q$$ and mass $$m$$ is projected from a point on the axis in a direction perpendicular to the axis. The maximum speed of the particle for which the particle does not strike the solenoid is
Earth's magnetic field always has a horizontal component except at