A solenoid of length $$50 \mathrm{~cm}$$ having 100 turns carries a current of $$2.5 \mathrm{~A}$$. The magnetic field at one end of the solenoid is

A circular coil of wire of radius $$r$$ has $$n$$ turns and carries a current $$I$$. The magnetic induction $$B$$ at a point on the axis of the coil at a distance $$\sqrt{3} r$$ from its centre is

Which of the following statements proves that Earth has a magnetic field ?

A copper rod $$A B$$ of length $$l$$ is rotated about end $$A$$ with a constant angular velocity $$\omega$$. The electric field at a distance $$x$$ from the axis of rotation is