Who proposed the principle of electromagnetic induction?

Describe the working of an $AC$ generator with the help of a labelled circuit diagram. What changes must be made in the arrangement to convert it to a $DC$ generator?

$A$ soft iron bar is introduced inside a current-carrying solenoid. The magnetic field inside the solenoid:

All the distribution circuits for domestic purposes are parallel connections.

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 $DC$.

If the key in the arrangement (Figure) is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane $ABCD$,the lines are