Assertion: A compass needle when placed on the magnetic north pole of the earth rotates in vertical direction.
Reason: The earth has only horizontal component of its magnetic field at the north poles.

Options

A. If both the assertion and reason are true and reason is a true explanation of the assertion.
B. If both the assertion and reason are true but the reason is not the correct explanation of assertion.
C. If the assertion is true is true but reason is false.
D. If both the assertion and reason are false.

Answer

D

Explanation

The earth has only vertical component of its magnetic field at the magnetic poles. Since compass needle is only free to rotate in horizontal plane. At north pole the vertical component of earth's field will exert torque on the magnetic needle so as to align it along its direction. As the compass needle cannot rotate in vertical plane, it will rest horizontally, when placed on the magnetic pole of the earth.