$(a)$ Describe an activity to show the pattern of magnetic field lines of a bar magnet,with the help of a cardboard piece and iron filings.
$(b)$ Compare the magnetic field of a bar magnet with that of a current-carrying solenoid with the help of a figure.

(N/A) Activity: Place a bar magnet on a sheet of white paper fixed on a drawing board. Sprinkle some iron filings uniformly around the bar magnet using a salt sprinkler. Gently tap the board. You will observe that the iron filings arrange themselves in a pattern representing the magnetic field lines of the bar magnet. The filings align along the field lines because each filing experiences a force in the magnetic field.
$(b)$ Comparison: The magnetic field lines produced by a current-carrying solenoid are very similar to those of a bar magnet. In both cases,the field lines emerge from the North pole and enter the South pole outside the magnet/solenoid. Inside,the field lines go from the South pole to the North pole. $A$ current-carrying solenoid behaves like a bar magnet with one end acting as the North pole and the other as the South pole.