Question

Earth's magnetic field always has a horizontal component except or Horizontal component of earth's magnetic field remains zero at

• A. Magnetic equator
• B. Magnetic Pole
• C. Graphical north pole
• D. At an altitude of 90^o

Answer 1

The correct option is B

Magnetic Pole

Explanation for the Correct option:

In case of option B:

1. The tangent to the magnetic field lines at a given position determines the direction of the earth's magnetic field at that location.
2. The value of the earth's magnetic field in the horizontal direction, that is in a direction parallel to the surface of the earth, is known as the horizontal component of the magnetic field.
3. The horizontal component is calculated by, $B_H=BCos\theta$ Where $B_H$ is the horizontal component, $B$ is Earth's magnetic field, and $\theta$ is the angle between Erath's magnetic field and horizontal component or $\theta$ is also known as the angle of dip.
4. The magnetic field lines, as well as the tangent to the field lines, are completely perpendicular to the earth's surface at the magnetic poles.
5. At magnetic poles angle of dip is $90°$
6. So, $B_H=BCos90\Rightarrow B_H=B\times 0\Rightarrow B_H=0$
7. As a result, the magnetic field at the magnetic poles is fully perpendicular to the earth's surface and so has no component that is parallel to the earth's surface.
8. As a result, except at the magnetic poles, the Earth's magnetic field always has a horizontal component.

Explanation for Incorrect options:

In case of option A:

1. At the magnetic equator, the angle of dip is $0°$
2. Horizontal component, $B_H=BCos0\Rightarrow B_H=B\times 1\Rightarrow B_H=B$.
3. At the magnetic equator, the value of the earth's horizontal component is maximum.
4. Hence option A is incorrect.

In case of option C:

1. At the geographic north pole, the angle of dip is $10°$
2. Horizontal component, $B_H=BCos10$
3. Hence option C is incorrect.

In case of option D:

1. Horizontal components do not have any relation to altitude.
2. Thus, option D is incorrect.

Hence, option B is the correct answer.