What does the direction of the thumb indicate in the Right-Hand Thumb Rule? In what way is this rule different from Fleming's Left-Hand Rule?

$(a)$ What is meant by a 'magnetic field'?
$(b)$ How is the direction of magnetic field at a point determined?
$(c)$ Describe an activity to demonstrate the direction of the magnetic field generated around a current-carrying conductor.
$(d)$ What is the direction of the magnetic field at the centre of a current-carrying circular loop?

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

An electric generator works on the principle of electromagnetic induction.

Commercial electric motors do not use

$(a)$ Define electromagnetic induction.
$(b)$ Two coils $P$ and $S$ are wound over the same iron core. Coil $P$ is connected to a battery and a key,and coil $S$ is connected to a galvanometer. Draw a suitable diagram of this arrangement and write your observations when:
$(i)$ current in the coil $P$ is started by closing the key.
$(ii)$ current continues to flow in coil $P$.
$(iii)$ current in coil $P$ is stopped by removing the key.
Explain the reason for such observations.