Assertion: If a compass needle be kept at magnetic north pole of the earth, the compass needle may stay in way direction.
Reason: Dip needle will stay vertical at the north pole of earth.

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

B

Explanation

We know that at magnetic poles the horizontal component of earth.s field is zero, only vertical component exists. So, as compass needle is free to rotate in horizontal plane and is thus effected by horizontal component only as H = ,0 hence, compass needle may stay in any direction. The dip needle rotates in a vertical plane and the angle of dip at poles is `90^(@)` . Hence, the dip needle will stand vertical at the north pole of earth