Question

Assertion: The magnetic poles of earth do not coincide with the geographic poles.
Reason: The discrepancy between the orientation of a compass and true north-south direction is known magnetic declination.
(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) Both Assertion and Reason are incorrect

Answer 1

Hint: To answer this question, we need to look into the definition of the geographic and the magnetic meridian. Then, we need to relate the position of a compass needle with the position of the magnetic meridian.

Complete answer:
A compass needle, when suspended freely, aligns itself in a particular direction. It happens due to the magnetic field of the earth. The north pole of the compass points towards the north pole of the earth’s magnetic field. This property is used for the determination of the north pole of the earth at a particular location.
But it is found that the north pole of the compass needle does not exactly point towards the geographic north pole of the earth. This is due to the fact that the line joining the magnetic poles is not aligned with the geographic axis. It is a little bit tilted with respect to the geographic axis. Thus the magnetic poles of the earth do not coincide with the geographic poles.
Therefore the Assertion is correct.
Now, the angle between the line joining the magnetic poles and the geographic axis is termed as magnetic declination. Since a compass aligns itself in the direction of the line joining the magnetic poles, so it gets tilted at the angle of the magnetic declination.
So we can say that the discrepancy between the orientation of a compass and true north-south direction is known as magnetic declination.
Therefore the Reason is also correct.
Now, as we can appreciate from above, the magnetic declination is the only reason for the deflection of the magnetic poles of the earth from the geographic axis.
So, the Reason is the correct explanation for Assertion.
Hence, the correct answer is option A.

Note:
The north pole of the earth’s magnetic field does not actually behave like the north pole of a bar magnet. We know that the magnetic field lines go into the north pole of a bar magnet. But the magnetic field lines actually come out of the magnetic north pole of earth. This is due to the convention which is accepted on the basis of the deflection of the north pole of a compass needle.