Question

The magnetic lines of force around a weak magnet are:
(a) Overlapping each other
(b) parallel lines
(c) not close continuous curves
(d) continuous curves

Answer 1

Hint: Magnetic Field Lines are closed continuous curves that never intersect at a point. We will check which of the given options satisfies these inherent properties of magnetic field lines.

Complete Answer:

We will analyse all the options one by one.
Option (a) says that magnetic field lines are overlapping each other. But we know that two magnetic field lines cannot cross each other as that will give two values for the magnetic field at one point which is not possible. It is because when 2 magnetic field lines cross, it is possible to draw 2 tangents at the point where they intersect. This will in turn give 2 different directions of the magnetic field at a single point. The direction of the magnetic field is tangent to the field line at any point in space. Hence, option(a) is wrong.

Option(b) says that magnetic field lines are parallel to each other. This is just the opposite of option(a). For magnetic field lines to not intersect with each other it is necessary that they remain parallel to each other at each point in the space. Hence, option(b) is correct.
Option(c) says that magnetic field lines are not close to continuous curves. But it is not true as magnetic field lines are continuous, forming closed loops without beginning or end. They go from the north pole to the south poles. It is because of the fact that magnetic monopoles do not exist so magnetic field lines can not have any origin or end, thus they form closed continuous loops. Hence, option(c) is wrong.
Option(d) says that magnetic field lines are continuous curves which is correct as magnetic field lines always form close continuous curves. Hence, option(d) is correct.
Therefore, the correct solution is option(a) and option(d).

Note: We often misinterpret magnetic lines of force as the lines which indicate the direction of magnetic force. This is completely wrong. Magnetic Lines of Force unlike what their name suggests are actually magnetic field lines. These magnetic field lines are imaginary lines tangent to which gives the direction for the magnetic field at a given point in the space. Thus, magnetic lines of force are the same as magnetic field lines and should not be confused with anything else or we might get conceptual questions like these wrong.