$(a)$ What are magnetic field lines? How is the direction of a magnetic field at a point determined?
$(b)$ Draw two field lines around a bar magnet along its length on its two sides and mark the field directions on them by arrow marks.
$(c)$ List any three properties of magnetic field lines.

(N/A) Magnetic field lines are the pictorial representation of a magnetic field. The direction of a magnetic field at a point is determined by placing a magnetic compass (or magnetic needle) at that point. The direction in which the north pole of the compass needle points gives the direction of the magnetic field at that point.
$(b)$ The field lines around a bar magnet are shown in the figure.
$(c)$ Properties of magnetic field lines are:
$(i)$ They emerge from the north pole and merge at the south pole outside the magnet.
$(ii)$ They are continuous closed curves.
$(iii)$ No two field lines can intersect each other.