Cause of Earth Magnetism – Earth’s Magnetism || Class 12 Physics Notes

Cause of Earth Magnetism

• Sir William Gilbert first suggested the existence of a powerful magnet inside the earth. This is not possible because.

(a) Temperature inside earth is so high that it will not be possible for magnet to retain magnetism.

(b) If there was a magnet inside the earth then position of earth’s magnetic poles would have not changed.

(c) The process of magnetization of this magnet is not understood.

• Grover suggested that earth’s magnetism is due to flow of current near outer surface of earth. These currents are produced due to sun. The hot air rising from regions near equator while going towards north and south hemispheres gets electrified. These then magnetize ferromagnetic materials near surface of earth.
• According to another view earth’s core has many conducting materials like iron and nickel in molten state. Conventional currents are produced in this semi fluid core due to rotation of earth about its axis which generates magnetism.
• Another view says magnetism is due to presence of ionized gases in atmosphere. The high energy sun rays ionize gas atoms in upper layer of atmosphere. The radioactivity of atmosphere and cosmic rays also ionize the gases. Strong electric currents flow due to rotation of earth producing magnetism.

Thus most likely cause of earth’s magnetism is the motion and distribution of charged materials in and outside the earth.

#### Geographic Axis

It is straight line passing through the geographic poles of the earth. It is the axis of rotation of the earth. It is known as polar axis.

#### Geographic Meridian

It is a vertical plane passing through geographic north and south poles of the earth.

#### Geographic Equator

A great circle on the surface of the earth in a plane perpendicular to geographical axis is called geographic equator. All places on geographic equator are at equal distances from geographical poles.

#### Magnetic Axis

It is a straight line passing through the magnetic poles of the earth. It is inclined to geographic axis at nearly $17^{\circ}$.

#### Magnetic Meridian

It is a vertical plane passing through the magnetic north and south poles of the earth.

#### Magnetic Equator

A great circle on the surface of the earth in a plane perpendicular to magnetic axis is called magnetic equator. All places on magnetic equator are at equal distance from magnetic poles.