The strength of the magnetic field inside a long current-carrying straight solenoid is

$(a)$ What is the function of an earth wire in electrical instruments? Why is it necessary to earth the metallic electric appliances?
$(b)$ Explain what is short-circuiting and overloading in an electric supply.
$(c)$ What is the usual capacity of the fuse wire in the line to feed:
$(i)$ lights and fans?
$(ii)$ appliances of $2 \,kW$ or more power?

Which instrument works on the principle of 'Electromagnetic induction'?

$(a)$ What is electromagnetic induction?
$(b)$ In what way can the magnitude of the induced current be increased?

How does the strength of the magnetic field at the centre of a circular coil of wire depend on: $(i)$ the radius of the coil $(ii)$ the number of turns of wire in the coil $(iii)$ the strength of the current flowing in the coil?

Identify the poles of the magnet in the given figure.