Question

In a plane perpendicular to the magnetic meridian, the dip needle will remain:
(A) Vertical
(B) Horizontal
(C) At $45^{\circ}$ from horizontal
(D) At $60^{\circ}$ from vertical

Answer 1

Hint: This question can easily be solved when we remember that the earth’s magnetic South Pole is towards the earth’s actual or geometrical North pole while the earth’s magnetic North pole is towards the earth’s actual or geometrical South pole. We have to now think where a magnetic needle would point when it is placed in a horizontal plane.

Complete step by step answer:
If a magnetic needle is placed in a horizontal plane, it would align itself along the earth’s magnetic North-South or the magnetic meridian. Now, there would be two vertical planes. One of them would pass through the magnetic meridian and the other would be perpendicular to it. If we place the needle in the vertical plane that passes through the magnetic meridian at the earth’s equator, then in this case the needle would show the horizontal direction.
However, if the needle were placed in the vertical plane that passes through the magnetic meridian at the earth’s equator, then in this case the needle would also show the horizontal direction. This happens because only horizontal fields are present there.
The angle of dip would change if the needle were to be placed in the geometric median. The vertical component would remain the same but the horizontal component would change. Thus, in a plane perpendicular to the magnetic meridian the dip needle would remain vertical.
Hence, the correct answer to this problem is (A).

Note: If the needle were to be placed in the vertical plane passing through the magnetic meridian but at any point other than the earth’s equator or poles, it would align itself in the direction of the resultant magnetic field.