Test: Earth's Magnetism - JEE MCQ

Three quantities are needed to specify the magnetic field of the earth on its surface, namely, the horizontal component, the magnetic declination and the magnetic dip. These are known as elements of the earth’s magnetic field or magnetic elements.

A vertical plane passing through the axis of a freely suspended or pivoted magnet is known as magnetic meridian of Earth. The vertical plane passing through the geographical North Pole and South Pole at a given place is known as the geographical meridian of that place.

Magnetic dip or inclination at a place is defined as the angle made by the Earth’s magnetic field with the horizontal in the magnetic meridian. It is denoted by δ.
Magnetic declination at a place is defined as the angle between the geographic meridian and magnetic meridian.

No, this statement is false. The Earth always has a vertical component except at the equator. Similarly, the earth always has a horizontal component except at the poles.

Horizontal component is a component of Earth’s magnetic field along the horizontal direction in the magnetic meridian. It is denoted by B_H. If B is the intensity of Earth’s total magnetic field, then the horizontal component of Earth’s magnetic field is given by:
B_H=Bcosδ

Angle of dip is 90^o at geographical North Pole because attraction on the North Pole of needle is very strong and the needle remains in vertical plane. At the magnetic equator, the needle will point horizontally, i.e. dip angle is 0^o. As you move from the magnetic equator towards the magnetic pole, the angle increases in the northern hemisphere. So, the angle of dip is maximum.

Given: H = 9 × 10^-5; R = 180 × 10^-6 = 18 × 10^-5
The required equation ➔ H=Rcosδ

Therefore, δ = cos^-1 1/2 

=60^o
Thus, the angle of dip is 60^o.

Yes, the angle of dip at a place is equal to 45^o, when the vertical and horizontal components of earth’s magnetic field are equal. In this case ➔ δ=45^o

So, B_V=B_H.

Given: Horizontal component (H) = 0.35 G; Angle of dip (δ) = 30^o
Required equation ➔ cosδ= H/B

Therefore, the magnitude of the magnetic field at that place is 0.40 G.

If a magnet is freely suspended or inclined or dipped, the angle between the horizontal and the angle of inclination of the magnet that is inclined only by the earth’s magnetic field will indicate the magnetic latitude. The relation is as follows:
tanδ=2tanλ