In the diagrams shown below:
$(i)$ Name the type of current in two cases.
$(ii)$ Identify any one source for each type of these currents.
$(iii)$ What is the frequency of current in case $(ii)$ in India?
$(iv)$ Use above graphs to write two differences between the current in two cases.

Whenever the magnetic field through a coil is changed,a potential difference is produced in the coil.

The horizontal component of the Earth's magnetic field at a place is uniform and its direction is from south to north. $A$ high current flows through a horizontal power line at this place from west to east. Consider two points $A$ and $B$ at equal distances from the wire,respectively above and below it. Giving reasons,explain where the magnetic field is stronger: at $A$ or at $B$.

What is meant by the term magnetic field lines? List any two properties of magnetic field lines.

The phenomenon of electromagnetic induction is:

State two ways by which the strength of an electromagnet can be increased.