Question

Assertion: At neutral point, a compass needle point out in any arbitrary direction
Reason: Magnetic field of earth is balanced by field due to magnets at the neutral point
A. Both assertion and reason are correct and reason is the correct explanation for assertion
B. Both assertion and reason are correct but reason is not the correct explanation for assertion
C. Assertion is correct but reason is incorrect
D. Bothe assertion and reason are incorrect

Answer 1

Hint: In a region where there are two magnetic fields, the points where the direction of one field is equal in magnitude and opposite in direction to the other magnetic field, the resultant magnetic field becomes zero. This can happen when a magnet is placed at some angle with the earth’s magnetic field.

Complete answer:
A bar magnet produces a magnetic field around it. The magnetic lines of force look like this.

Outside the magnet, the lines start from the north pole and end at the south pole of the magnet while inside the magnet, they start at the south pole and end at the north pole.
Even if this magnet is kept in isolation from other magnetic fields, there is a magnetic field of earth always around it. The points horizontal where the horizontal component of earth’s magnetic field has equal magnitude and opposite direction to the field of the bar magnet, the two fields cancel each other and resultant magnetic field intensity at those particular points is zero. These points are called neutral points. Neutral points can be observed between any two fields interacting with each other and not just the magnetic field of earth.
When the poles of the bar magnet are aligned with the poles of earth’s magnetic field then we observe two neutral points on either side of the magnet. When a magnetic compass is placed at the neutral points, it comes to rest in any random direction.
From this discussion, we can say that both the assertion and the reason are correct and the reason is the correct explanation of the assertion.

The correct option is A.

Note:
To obtain the neutral points on either side of the magnet, the alignment of the magnet in earth’s magnetic field is done in such a way that magnet’s north points to earth’s magnetic south and the magnet is parallel to the magnetic meridian of earth. The points at which the magnetic needle points in a random direction represents a neutral point.