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 assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false.
D. If the assertion and reason both 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 can not rotate in vertical plane it will rest horizontally when placed on the magnetic pole of the earth.