An alternating electric current has a frequency of $50 \ Hz$. How many times does it change its direction in one second (in $\times$)?

The principle of which of these devices is based on electromagnetism?

How is the strength of the magnetic field at a point near a wire related to the strength of the electric current flowing in the wire?

Draw an appropriate schematic diagram showing common domestic circuits and discuss the importance of a fuse. Why is it that a burnt-out fuse should be replaced by another fuse of identical rating?

What is a fuse? How does it function?

$(a)$ When do we state that an electrical appliance is earthed? Mention the function of the earth wire in electric lines. Why is it necessary to earth electric appliances having a metallic body?
$(b)$ Explain what is short-circuiting and overloading in an electric supply.