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

$(a)$ What is the direction of magnetic field lines inside a bar magnet and outside of it?
$(b)$ What does the degree of closeness of the field lines represent?

According to the Right-Hand Thumb Rule,what does the thumb indicate?

$A$ compass needle is placed near a current-carrying wire. State your observation for the following cases and give the reason for the same in each case:
$(a)$ Magnitude of electric current in the wire is increased.
$(b)$ The compass needle is displaced away from the wire.

Which of the following statements is $NOT$ true regarding the magnetic field lines of a bar magnet?

In the arrangement shown in the figure,there are two coils wound on a non-conducting cylindrical rod. Initially,the key is not inserted. Then the key is inserted and later removed. Then