By placing an iron-like metal inside the solenoid,its magnetic field becomes $......$

$(a)$ 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.

How is the relative strength of a magnetic field shown around a magnet?

How does a current-carrying solenoid behave?

The strength of the magnetic field inside a long current-carrying straight solenoid is

What are magnetic field lines? How is the direction of magnetic field at a point determined? Mention two important properties of magnetic field lines.