$A$ device used for producing current is:

$(a)$ Magnetic field lines of two bar magnets $A$ and $B$ are as shown below. Name the poles of the magnets facing each other.
$(b)$ Two magnetic field lines never intersect each other. Why?
$(c)$ How does the strength of the magnetic field at the centre of a current-carrying circular coil depend on the
$(i)$ radius of the coil,
$(ii)$ number of turns in the coil, and
$(iii)$ strength of the current flowing in the coil?

Draw a labelled circuit diagram of a simple electric motor and explain its working. In what way are these simple electric motors different from commercial motors?

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?

Name some devices in which electric motors are used.

The branch of science that covers the comprehensive study of electricity and magnetism is known as $.........$.