Earth's Magnetic Field: Cause, Theory & Components

The Earth's magnetic field is the magnetic field that extends from the inside of the Earth into space, where it interacts with the solar wind, a stream of charged particles emitted by the Sun.

• It is also known as the Geomagnetic field.
• The magnetic field is created by electric currents induced by the movements of convection currents of molten iron and nickel in Earth's outer core.
• These convection currents are caused by heat escaping from the core, which is a natural phenomenon known as a geodynamo.
• At the surface, the magnitude of the Earth's magnetic field ranges from 25 to 65 T (0.25 to 0.65 G).
• It is approximated by a magnetic dipole field that is now inclined at an angle of around 11° with regard to the Earth's rotating axis.
• The North magnetic pole of the Earth actually represents the South pole of Earth's magnetic field, while the South geomagnetic pole is the North pole of Earth's magnetic field.

Key Terms: Earth's Magnetism, Dynamo Effect, Magnetic-field Strength, Magnet, Bar Magnet, Electric Current, Magnetic Pole

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What Is Earth’s Magnetic Field?

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The Earth's magnetic field, also known as the geomagnetic field, is formed in our planet's interior and reaches into space, forming the magnetosphere.

• Life on Earth would be impossible without the magnetic field, which protects us from the constant attack of charged particles generated by the sun known as the solar wind.
• The Earth has two poles: the geographic pole and the magnetic pole.
• Imagine a huge bar magnet within our planet as roughly aligned with the Earth's axis, to represent the magnetic field.
• Each end of the magnet is quite near the geographic North and South poles (approximately 11 degrees).
• At each magnetic pole, the Earth's invisible magnetic field lines move in a closed, continuous loop and are almost vertical.
• The Earth's magnetic field stretches millions of kilometers into space and resembles a bar magnet. The earth's magnetic pole is positioned between the Northern Pole and the North Pole's Antarctic magnets.
• That is why a compass magnet's north pole points north (north and south poles attract). 

Read More: Magnetism and Matter Important Questions

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Dynamo Effect

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It is not a clear theory of the Earth’s magnetism as to what causes the Earth to have its own magnetic field.

• Initially, the magnetic field was visualized as a gigantic bar magnet located approximately along the axis of rotation of the earth and within its center.
• Obviously, that was way too simple to explain away. 
• Now, the Dynamo Effect states that the Earth’s magnetic field has emerged because of the presence of metallic fluids like molten iron and nickel in the outer core of the planet.
• The convective motion of these fluids produces an electric current, causing the magnetic field to arise. 

Related Topics to Magnetism:

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What Causes the Earth's Magnetism?

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The Earth's magnetism is generated by molten iron and nickel convection currents in the Earth's core. Charged particles in these currents generate magnetic fields.

• The sun also releases ionizing charged particles towards the earth known as solar winds.
• The earth’s magnetic field deflects these particles and prevents them from entering the atmosphere. 
• Had this magnetic shield not been present, solar winds would have eroded our atmosphere rendering life inhabitable on Earth.
• An example of this is Mars, where the absence of a magnetic field has created an atmosphere unable to sustain life. 
• The magnetic poles and the geographical north and south poles of the Earth are not aligned with each other.
• This means that the southern magnetic pole is in Canada, while the northern magnetic pole is in Antarctica.
• The magnet poles have around an 11^o inclination to the rotational axis.

Read More: SI unit of Magnetic Field

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Components of the Earth's Magnetic Field

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Three components determine the magnitude and direction of the Earth's magnetic fields: 

1. Magnetic Declination
2. Magnetic inclination (angle of dip)
3. The horizontal component of the Earth’s magnetic field

Magnetic Declination 

The angle between the true north and the magnetic north is known as the magnetic declination. The true north is never constant; its position keeps changing based on the earth’s surface and time.

Magnetic Inclination

Also known as the angle of dip, the magnetic inclination is the angle formed by the horizontal plane on the earth’s surface. The angle of dip at the magnetic equator is 0° and 90o at the magnetic poles. 

Horizontal Component of Earth's Magnetic Field 

Two factors account for the intensity of the Earth's magnetic field: 

• Horizontal component (H) 
• Vertical Component (v)

Various Components and its Definition

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Solved Examples

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Ques. Calculate the vertical component of the earth’s magnetic field at the equator if the horizontal component of the earth’s magnetic field is at B and the angle of dip is 60°.

Ans. The horizontal component of the earth’s magnetic field, H = Be cos 60° = B

Be x ½ = B

Be = 2B

The vertical component of the earth’s magnetic field, V = Be sin 60°

V = 2B x √3/2

V = √3B

Ques. Calculate the angle of dip for a place whose horizontal and vertical components of the earth’s magnetic field are equal.

Ans. The angle of dip is, δ = tan-1(BV/BH)

BV is the vertical component of the Earth’s magnetic field

BH is the horizontal component of the Earth’s magnetic field

BV = BH

δ = tan-1(1) = 45° = angle of dip

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Previous Year Questions 

1. An electron in motion is associated with… [ KCET 1996]
2. Two parallel wires carry electric current in same direction. The wires... [ KCET 1996]
3. Resistance of an ideal ammeter is...[ KCET 1996]
4. If a current of 0.1 A is passed through the coil, what is the couple acting?...[CBSE Class 12 ]
5. The acceleration of the falling magnet is..[NEET]
6. A bar magnet is equivalent to ............[KCET 2004]
7. A metal ring is held horizontally and bar magnet is dropped through….[NEET]
8. The total charge, induced in a conducting loop when it is moved in magnetic field depend on...[NEET 1992]
9. If a charge particle enters perpendicular in the uniform magnetic field, then...[JIPMER 2016]
10. Who invented the cyclotron?
11. When a charged particle moving with velocity is….
12. The angle of dip at a place is….
13. The associated magnetic moment is given by….
14. A uniform electric field and a uniform magnetic field are produced…
15. Ampere’s circuital law can be derived from…..
16. If a magnetic dipole of moment M situated in the direction of …
17. If the susceptibility of dia, para and ferro magnetic materials are ….
18. Materials suitable for permanent magnet, must have which of the following properties ?
19. At what temperature, the ferromagnetic substances become paramagnetic ?
20. a magnetic induction of strength at its centre is...