List three sources of magnetic fields.

The strength of the induced potential difference depends on the relative speed between the coil and the magnet.

Under what condition does a current-carrying conductor kept in a magnetic field experience maximum force? On what other factors does the magnitude of this force depend? Name and state the rule used for the determination of the direction of this force.

Answer the following questions:
$(i)$ What is the direction of magnetic field lines outside a bar-magnet?
$(ii)$ Why two magnetic field lines cannot intersect each other?
$(iii)$ What is indicated by crowding of magnetic field lines in a given region?
$(iv)$ What is the frequency of $AC$ in India?
$(v)$ State one advantage of $AC$ over $DC$.

What constitutes the field of a magnet?

What is the shape of the magnetic field lines inside a solenoid?