Question

Earth’s magnetic field always has a horizontal component except at

• A. equator
• B. magnetic poles
• C. a latitude of 60°
• D. an altitude of 60°

Answer 1

The Correct Option is B

Understanding Earth's Magnetic Field

Earth's magnetic field is a vector field, meaning it has both magnitude and direction at every point in space. At any location on Earth's surface, the magnetic field can be described by two components in the horizontal plane and one component in the vertical plane.

Horizontal Component (H): This component is in the horizontal plane, typically oriented geographically North-South and East-West.

Vertical Component (V): This component is perpendicular to the horizontal plane, pointing either upwards or downwards.

The angle between the total magnetic field and the horizontal component is called the angle of dip or magnetic inclination ($\delta$).

The horizontal component (H) and vertical component (V) are related to the total magnetic field (B) and the angle of dip ($\delta$) as follows:

$H = B \cos \delta$

$V = B \sin \delta$

Condition for Zero Horizontal Component

For the horizontal component (H) to be zero, we must have:

$H = B \cos \delta = 0$

Since the Earth's magnetic field strength (B) is generally non-zero, for H to be zero, $\cos \delta$ must be zero.

$\cos \delta = 0$ when $\delta = 90^\circ$ or $\delta = -90^\circ$.

Angle of Dip at Different Locations on Earth

Magnetic Equator: At the magnetic equator, the Earth's magnetic field lines are horizontal. Therefore, the angle of dip ($\delta$) is $0^\circ$. In this case, $H = B \cos 0^\circ = B$, which is the maximum horizontal component.

Magnetic Poles: At the magnetic poles, the Earth's magnetic field lines are vertical.

- At the Magnetic North Pole, the magnetic field lines point vertically downwards into the Earth. The angle of dip is $+90^\circ$.

- At the Magnetic South Pole, the magnetic field lines point vertically upwards out of the Earth. The angle of dip is $-90^\circ$.

At the magnetic poles, since $\delta = \pm 90^\circ$, the horizontal component $H = B \cos (\pm 90^\circ) = B \times 0 = 0$. Thus, at the magnetic poles, the Earth's magnetic field is purely vertical, and there is no horizontal component.

Latitude of 60° and Altitude of 60°: At any latitude other than the magnetic equator or magnetic poles, there will be both horizontal and vertical components of Earth's magnetic field. Altitude above the Earth's surface does not drastically change the direction of the Earth's magnetic field at a particular location on the surface.

Final Answer: Earth's magnetic field always has a horizontal component except at the magnetic poles, where the field is purely vertical and the horizontal component is zero.

Answer 2

Earth's magnetic field always has a horizontal component except at the magnetic poles. At the magnetic poles, the field lines are vertical, so there is no horizontal component. The horizontal component is maximum at the equator and decreases as we move towards the poles where it becomes 0. Altitude does not change the fact that there is a horizontal component unless the altitude is 0 (i.e. at the magnetic poles of the Earth)

The correct answer is (B) magnetic poles.