Magnetic Field Earth Magnetism - Definition, Cause, Theory, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:52 PM IST

A compass is helpful to find the directions and the needle inside the compass always points in the north direction. The compass could be traditionally used as a mechanical compass or inbuilt smartphone component or a refrigerator magnet, all of these points towards the north direction. Do you know why it is so? What's the reason behind it? It is because of Earth’s magnetism. In this article, we will discuss what is the Earth's magnetic field, the components of Earth's magnetic field, the Earth's magnetic poles, the magnetic field of Earth diagram, the Dynamo effect, the horizontal component of Earth magnetic field formula, and equations related to Earth's magnetic field.

This Story also Contains

What is the Earth's Magnetic Field
Dynamo Effect - The Cause of Earth Magnetism Class 12
Earth's Magnetic Poles
Magnetic Declination
The Angle of Dip
Horizontal Component of Earth Magnetic Field Formula
Equations Related to Earth's Magnetic Field Class 12

Magnetic Field Earth Magnetism - Definition, Cause, Theory, FAQs

What is the Earth's Magnetic Field

The Earth's magnetic field is the magnetic field that surrounds Earth. It is formed due to the Dynamo effect where it is formed by the movement of molten iron and nickel in the outer core. The magnetic field is found to be the component that is similar to a protective layer around the Earth. This magnetic field of the earth does not allow the unwanted charged particles of the sun by repelling and trapping the particles and unwanted wave signals. The magnetic field of the planet is not only present inside the Earth but, also extends for some millions of kilometers outside the Earth's diameter and the whole Earth acts like a bar magnet. The magnetic field has a very weak force compared with other fundamental forces.

Dynamo Effect - The Cause of Earth Magnetism Class 12

The theory which gives a good explanation of the cause of the earth's magnetic system is known as the Dynamo effect. The Dynamo effect explains that the Earth maintains the magnetic field lines on its own due to the metallic fluids that are present in both the outer and inner core of the Earth. Molten iron is present in the outer core and the solidified elements present in the inner core play an important role in the cause of Earth's magnetism.

Some convection currents which are formed by the molten iron and the nickel of the earth's core produce the Earth’s magnetic field. These convection currents carry very few streams of charged particles which causes the magnetic field. The deflection of the magnetic field is caused due to the solar wind caused by the Sun and prevents the entry of these solar winds into our atmosphere. If the magnetic field is removed from the Earth, then these solar winds could destroy the whole Earth, and life would not exist on Earth. The planet Mars lacks these magnetic fields and this is the reason life does not exist on the planet Mars. The magnetic field of Earth diagram is given below.

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the earth's magnetic field and magnetic poles are well depicted

Earth's Magnetic Poles

The poles of these magnetic fields are inclined by 10 degrees to the rotational axis of the Earth i.e. instead of aligning in the actual geographic north-south direction, the Earth's magnetic pole of the south is present near Canada, and the Earth's magnetic pole of the north is present in Antarctica.

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The Components of Earth's Magnetic Field

The magnitude and direction of the earth's magnetism are calculated by using the three major components. The three components are listed below.

Magnetic declination
The angle of dip (which is known as magnetic inclination)
Earth's magnetic field’s horizontal component

Let us discuss the components in detail.

Magnetic Declination

The concept of magnetic declination gives us the angle that lies between the magnetic north and true north. The fact is, this true north does not have a fixed or constant position on the horizontal plane. It varies according to the surface of the earth and time.

The Angle of Dip

The angle of dip is also called magnetic inclination. This magnetic inclination is an angle that is caused by the plane horizontal to the earth’s surface. This magnetic inclination angle is found to be 0 degrees at the magnetic equator of the earth and the magnetic inclination angle at the magnetic poles is found to be 90 degrees.

Horizontal Component of Earth Magnetic Field Formula

The intensity of the magnetic field of the earth breaks into two different components, i.e. horizontal component and a vertical component.

$\tan \bar{\delta}=\frac{\mathrm{B}_{(\mathrm{v})} }{ \mathrm{B}(\mathrm{h})}$

$\sin \bar{\delta}=\frac{B_{(v)} }{ B}$

$\cos \bar{\delta}=\frac{B_{(h)} }{ B}$

$\sin ^2 \bar{ \delta}+\cos ^2 \bar{ \delta}=\frac{B^2_{(\mathrm{v})}}{ \mathrm{B}^2}+\frac{\mathrm{B}_{(\mathrm{h})}^{2} }{\mathrm{B}^2}$

$B=\sqrt{B_{(h)}^2+B_{(v)}^2}$

Where B represents the total magnetic field intensity or strength and is a vector component.

B can be also written as follows.s

$B=\sqrt{X^2+Y^2+Z^2}$

Where, X, Y, and Z represent the components of the magnetic field along the geographic north,

geographic east and vertically downward direction respectively.

X and Y can be found out by using the below formula

$\mathrm{X}=\mathrm{H} \cos \alpha$ and $\mathrm{Y}=\mathrm{H} \sin \alpha$

Where H represents the component of the magnetic field that is parallel to the surface of the earth and this H is equal to $\sqrt{X^2+Y^2}$

The magnetic declination angle (which is known as the angle between true and magnetic north) is denoted by $\alpha$, and this $\alpha$ is equal to $\tan ^{-1}\left(\frac{Y}{X}\right)$. The magnetic inclination angle (which is known as the angle of the horizontal component of the magnetic field) is denoted by $\theta$, and this $\theta$ is equal to $\tan ^{-1}\left(\frac{Z}{H}\right)$.

Equations Related to Earth's Magnetic Field Class 12

Equation	Formula
Magnetic Dip (Inclination)	$\tan I=\frac{B_v}{B_h}$
Total Magnetic Field Strength	$B=\sqrt{B_h^2+B_v^2}$
Magnetic Declination	$D=\theta-\theta_m$ (No fixed formula; location-based)
Horizontal Component of Magnetic Field	$B_h=B \cos I$
Vertical Component of Magnetic Field	$B_v=B \sin I$
Gauss's Law for Magnetism	$\oint \mathbf{B} \cdot d \mathbf{A}=0$
Magnetic Potential due to Dipole	$V=\frac{\mu_0 m}{4 \pi r^3}(2 \cos \theta)$
Magnetic Field due to a Dipole (Radial)	$B_r=\frac{\mu_0}{4 \pi} \frac{2 m \cos \theta}{r^3}$
Magnetic Field due to a Dipole (Tangential)	$B_\theta=\frac{\mu_0}{4 \pi} \frac{m \sin \theta}{r^3}$

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Frequently Asked Questions (FAQs)

1. What is the horizontal component of the earth magnetic field value?

The value of the component of the earth’s magnetic field which is horizontal is found to be zero.

2. What is the earth magnetic field value (in terms of nT)?

The earth magnetic field value lies around 25,000 nT to 65,000 nT.

3. What is known as the earth's magnetosphere?

The system of magnetic fields that are covered and surrounded by the atmosphere of the Earth is known as the earth's magnetosphere.

4. Define magnetic compass

Magnetic compass direction-finding device in which the needle always points to the north direction and helps us to find the direction on Earth.

5. Why does the earth have a magnetic field?

The deflection of the magnetic field is caused due to the solar wind caused by the Sun and prevents the entry of these solar winds into our atmosphere. If the magnetic field is removed from the Earth, then these solar winds could destroy the whole earth and life would not exist on Earth. This is why the earth requires a magnetic field.

6. What is the dynamo effect?

The Dynamo effect tells us that the Earth includes the magnetic field lines on its own due to the metallic fluids which are present in both the outer and inner core of the earth. Molten iron is present in the outer core and the solidified magnetic elements of earth present in the inner core plays an important role in the cause of Earth

7. How is Earth's magnetic field different from a bar magnet's field?

While Earth's magnetic field is often compared to a bar magnet, there are key differences. Earth's magnetic field is generated by complex processes in its core, not by permanent magnetization. Additionally, Earth's magnetic poles are not aligned exactly with its geographic poles and can shift over time. The field is also not symmetrical and is influenced by factors like solar wind.

8. What causes Earth's magnetic field?

Earth's magnetic field is primarily generated by the geodynamo process in the planet's outer core. This involves the movement of liquid iron and nickel in the outer core, which creates electric currents. These currents, combined with Earth's rotation, produce the magnetic field through a self-sustaining process called the dynamo effect.

9. What is Earth's magnetic field?

Earth's magnetic field is a naturally occurring phenomenon that surrounds our planet, extending from its interior out into space. It acts like a giant magnet, with field lines running from the magnetic south pole to the magnetic north pole. This field protects Earth from harmful solar radiation and plays a crucial role in navigation for both humans and animals.

10. Can Earth's magnetic field change over time?

Yes, Earth's magnetic field can and does change over time. This includes both short-term fluctuations and long-term changes. The most dramatic change is magnetic reversal, where the north and south magnetic poles switch positions. This has happened many times in Earth's history, with the last reversal occurring about 780,000 years ago.

11. What would happen if Earth's magnetic field disappeared?

If Earth's magnetic field disappeared, the planet would lose its primary defense against solar radiation. This would lead to increased exposure to cosmic rays and solar wind, potentially damaging satellites, disrupting power grids, and harming living organisms. The atmosphere could be gradually stripped away by solar wind, similar to what happened to Mars.

12. What is magnetic declination?

Magnetic declination is the angle between magnetic north (the direction a compass needle points) and true north (the direction to the geographic North Pole). This angle varies depending on your location on Earth and changes over time due to the movement of the magnetic poles. Navigation systems must account for magnetic declination to provide accurate directions.

13. How does the Earth's magnetic field protect us?

Earth's magnetic field acts as a shield against harmful solar radiation and charged particles from space. It deflects most of the solar wind, a stream of charged particles from the Sun, around the planet. This protection is crucial for life on Earth, as it prevents the solar wind from stripping away our atmosphere and exposing the surface to dangerous levels of radiation.

14. What are the Van Allen radiation belts?

The Van Allen radiation belts are regions of energetic charged particles that are held in place by Earth's magnetic field. There are two main belts: an inner belt consisting mostly of protons, and an outer belt consisting mainly of electrons. These belts trap harmful radiation from space, providing additional protection for life on Earth.

15. How do animals use Earth's magnetic field for navigation?

Many animals, including birds, sea turtles, and some mammals, can detect Earth's magnetic field and use it for navigation. This ability, called magnetoreception, allows them to orient themselves and navigate over long distances. Some animals may have magnetic particles in their bodies that act like tiny compasses, while others may use quantum effects in their eyes to "see" the magnetic field.

16. What is a geomagnetic storm?

A geomagnetic storm is a temporary disturbance of Earth's magnetosphere caused by a solar wind shock wave or solar magnetic field that interacts with Earth's magnetic field. These storms can cause auroras, disrupt radio communications, and in severe cases, damage electrical grids and satellites.

17. How do scientists measure Earth's magnetic field?

Scientists use various instruments to measure Earth's magnetic field, including magnetometers on the ground, in aircraft, and on satellites. Ground-based observatories provide continuous measurements at fixed locations, while satellite measurements give a global picture of the field. Paleomagnetists also study the magnetic properties of rocks to understand the field's history.

18. What is the difference between the geomagnetic poles and the magnetic poles?

Geomagnetic poles are the points where the axis of a theoretical dipole (bar magnet) that best fits Earth's magnetic field intersects the surface. Magnetic poles, on the other hand, are the points where the magnetic field lines are perpendicular to the surface. The geomagnetic poles are calculated mathematically, while the magnetic poles are observed directly and can move more erratically.

19. How fast does Earth's magnetic north pole move?

The magnetic north pole moves at a variable rate. In recent years, its movement has accelerated. From the 1990s to 2005, it moved at an average rate of 10 km per year. However, since then, it has sped up to about 50-60 km per year, moving from the Canadian Arctic towards Siberia.

20. What is magnetic inclination or magnetic dip?

Magnetic inclination, also known as magnetic dip, is the angle that Earth's magnetic field lines make with the horizontal plane at any point on Earth's surface. At the magnetic equator, the inclination is zero (field lines are horizontal). At the magnetic poles, the inclination is 90° (field lines are vertical).

21. How does the strength of Earth's magnetic field vary across the planet?

The strength of Earth's magnetic field varies across the planet's surface. It is generally strongest near the poles and weakest near the equator. However, there are also regional variations, including areas of unusually weak field strength, such as the South Atlantic Anomaly.

22. What is the South Atlantic Anomaly?

The South Atlantic Anomaly is a region where Earth's inner Van Allen radiation belt comes closest to the planet's surface. This results in an increased flux of energetic particles in this area. It's caused by the non-concentricity of Earth's magnetic and rotational axes and the offset of the magnetic dipole from Earth's center.

23. How do solar flares affect Earth's magnetic field?

Solar flares can cause significant disturbances in Earth's magnetic field. When a solar flare releases a burst of charged particles (coronal mass ejection) that reaches Earth, it can compress the magnetosphere on the day side and extend it on the night side. This can lead to geomagnetic storms, affecting radio communications, navigation systems, and potentially damaging electrical grids.

24. What is the magnetosphere?

The magnetosphere is the region around Earth that is influenced by the planet's magnetic field. It extends from about 60,000 km on the side facing the Sun to over 300,000 km on the opposite side. The magnetosphere deflects most of the solar wind and cosmic rays, playing a crucial role in protecting Earth from harmful space radiation.

25. How does Earth's magnetic field compare to other planets in our solar system?

Earth's magnetic field is relatively strong compared to most other planets in our solar system. Jupiter and Saturn have much stronger fields due to their larger size and faster rotation. Mars and Venus have very weak fields, with Mars having only localized magnetic areas. Mercury has a weak global field, while the gas giants Uranus and Neptune have strong but oddly oriented magnetic fields.

26. How do we know about the history of Earth's magnetic field?

Scientists study the history of Earth's magnetic field through paleomagnetism. When rocks form, magnetic minerals within them align with the Earth's magnetic field at that time. By studying these rocks, scientists can determine the direction and strength of the magnetic field at different points in Earth's history, including past magnetic reversals.

27. What is a magnetic anomaly?

A magnetic anomaly is a local variation in Earth's magnetic field that differs from the expected value based on a global magnetic model. These anomalies can be caused by variations in the composition of Earth's crust, the presence of magnetic minerals, or large metallic objects. Magnetic anomaly maps are used in geological exploration and to locate buried objects.

28. What is magnetic reconnection?

Magnetic reconnection is a process where magnetic field lines from different magnetic domains are spliced to one another, changing their patterns of connectivity with respect to the sources. In Earth's magnetosphere, it occurs when the interplanetary magnetic field (IMF) carried by the solar wind connects with Earth's magnetic field, allowing energy from the solar wind to enter Earth's magnetosphere.

29. How do auroras relate to Earth's magnetic field?

Auroras, also known as the Northern and Southern Lights, are directly related to Earth's magnetic field. They occur when charged particles from the solar wind are guided by Earth's magnetic field lines towards the poles. These particles collide with atoms and molecules in the upper atmosphere, exciting them and causing them to emit light, creating the colorful auroral displays.

30. What is the difference between magnetic field intensity and magnetic field inclination?

Magnetic field intensity refers to the strength of the magnetic field, measured in units like tesla or gauss. Magnetic field inclination, on the other hand, is the angle that the magnetic field lines make with the horizontal plane at a given point on Earth's surface. While intensity tells you how strong the field is, inclination tells you about its direction relative to the ground.

31. How does the Earth's magnetic field interact with the solar wind?

The Earth's magnetic field interacts with the solar wind by creating a bow shock, similar to the wave created by a boat moving through water. This bow shock slows down and deflects much of the solar wind around the Earth. The region where the solar wind and Earth's magnetic field interact is called the magnetopause, which is constantly in flux due to variations in solar wind pressure.

32. How does the Earth's magnetic field affect space weather?

Earth's magnetic field plays a crucial role in space weather by interacting with and modulating the effects of solar activity. It shields Earth from much of the solar wind but can also channel charged particles towards the poles. During solar storms, the interaction between the enhanced solar wind and Earth's magnetic field can lead to geomagnetic storms, affecting satellite operations, radio communications, and power grids.

33. How do scientists predict changes in Earth's magnetic field?

Scientists predict changes in Earth's magnetic field using a combination of observational data and computer models. They collect data from ground-based observatories, satellites, and studies of magnetic minerals in rocks. This data is then used to create complex mathematical models of the Earth's core and its dynamics. These models can simulate the geodynamo process and project how the field might change in the future. However, predicting long-term changes, such as pole reversals, remains challenging due to the complex nature of the Earth's core processes.

34. How does the Earth's magnetic field affect radio communications?

Earth's magnetic field significantly impacts radio communications in several ways. It helps to reflect certain radio waves back to Earth, allowing long-distance communication. The ionosphere, a layer of charged particles held in place by the magnetic field, plays a crucial role in this process. However, during geomagnetic storms caused by solar activity, disturbances in the magnetic field can disrupt radio signals, particularly at high latitudes. Understanding these effects is crucial for maintaining reliable global communication systems.

35. How do compasses work in relation to Earth's magnetic field?

Compasses work by aligning themselves with Earth's magnetic field. A typical compass contains a magnetized needle that is free to rotate. The needle aligns itself with the horizontal component of Earth's magnetic field, pointing towards magnetic north. However, because magnetic north is not the same as geographic north, compass users need to account for magnetic declination to navigate accurately. The effectiveness of a compass can also be affected by local magnetic anomalies and variations in the Earth's field.

36. What is the role of Earth's magnetic field in the formation of the magnetotail?

The magnetotail is an extended region of Earth's magnetosphere on the side facing away from the Sun. It's formed as the solar wind stretches Earth's magnetic field lines on the night side of the planet. The magnetotail plays a crucial role in storing and releasing energy from the solar wind. During geomagnetic substorms, energy stored in the magnetotail is released, causing phenomena like auroras. The structure and dynamics of the magnetotail are directly influenced by the strength and configuration of Earth's magnetic field.

37. What is geomagnetic jerks?

Geomagnetic jerks are abrupt changes in the rate of change of Earth's magnetic field. These events occur over a period of a few months to a year and are observed in the east-west component of the field. The cause of these jerks is not fully understood but is thought to be related to sudden changes in the flow patterns of the liquid outer core. Studying these jerks provides insights into the dynamics of Earth's core and the processes that generate the magnetic field.

38. How does Earth's magnetic field affect the behavior of charged particles in the atmosphere?

Earth's magnetic field significantly influences the behavior of charged particles in the atmosphere. It traps and guides these particles, creating the Van Allen radiation belts. The field also directs charged particles from the solar wind towards the poles, leading to aurora formations. In the ionosphere, the magnetic field affects the movement of ions and electrons, influencing radio wave propagation. Understanding these interactions is crucial for satellite operations, radio communications, and studying space weather effects.

39. What is the difference between induced and remanent magnetization in rocks?

Induced magnetization occurs when a rock is exposed to an external magnetic field, such as Earth's current field. This magnetization disappears when the external field is removed. Remanent magnetization, on the other hand, is the permanent magnetization retained by a rock after the external field is removed. It's acquired when magnetic minerals in the rock align with the Earth's field as the rock forms or cools below its Curie temperature. Studying remanent magnetization in rocks is crucial for understanding the history of Earth's magnetic field.

40. How do scientists determine the age of rocks using Earth's magnetic field?

Scientists use a technique called magnetostratigraphy to determine the age of rocks based on Earth's magnetic field history. This method relies on the fact that the Earth's magnetic field has reversed polarity many times throughout geological history. When rocks form, they record the orientation of the magnetic field at that time. By comparing the magnetic properties of rock layers to the known timeline of Earth's magnetic reversals, scientists can estimate the age of the rocks. This technique is particularly useful when used in conjunction with other dating methods.

41. What is the Curie point and how does it relate to Earth's magnetic field?

The Curie point, or Curie temperature, is the temperature above which materials lose their permanent magnetic properties. For the minerals that contribute to Earth's magnetic field, this temperature is reached at depths of about 20-30 km below the surface, in a region known as the Curie depth. Below this depth, rocks cannot retain

42. How does Earth's rotation affect its magnetic field?

Earth's rotation plays a crucial role in generating and maintaining its magnetic field. The Coriolis effect, caused by Earth's rotation, helps organize the flow of liquid iron in the outer core into columns parallel to the rotation axis. This organized flow is essential for the self-sustaining dynamo process that generates the magnetic field.

43. What is magnetic flux?

Magnetic flux is a measure of the total magnetic field passing through a given area. In the context of Earth's magnetic field, it represents the strength and density of the field lines passing through a particular region of space or a surface on Earth. Changes in magnetic flux over time can induce electric currents, which is the principle behind electromagnetic induction.

44. What is the difference between the dipole and non-dipole components of Earth's magnetic field?

Earth's magnetic field can be divided into dipole and non-dipole components. The dipole component is the part that resembles the field of a bar magnet and accounts for about 90% of the field at the Earth's surface. The non-dipole component represents the remaining variations and complexities in the field that cannot be explained by a simple dipole model. These non-dipole components are important for understanding local variations and changes in the field over time.

45. What is the relationship between Earth's magnetic field and plate tectonics?

While Earth's magnetic field is primarily generated in the core, it interacts with and is influenced by plate tectonics. The movement of tectonic plates affects the distribution of magnetic minerals in the crust, creating local magnetic anomalies. Additionally, the study of paleomagnetism in rocks formed at different times has been crucial in understanding plate tectonic movements throughout Earth's history. The magnetic field recorded in these rocks provides evidence for continental drift and helps reconstruct past plate configurations.

46. What is magnetic secular variation?

Magnetic secular variation refers to the gradual, long-term changes in Earth's magnetic field over time. These changes occur in both the strength and direction of the field and can vary from place to place on Earth's surface. Secular variation is caused by changes in the flow patterns of the liquid outer core. Monitoring these variations is important for updating navigational charts and understanding the dynamics of Earth's interior.

47. How does the strength of Earth's magnetic field compare to artificial magnets?

Earth's magnetic field is relatively weak compared to artificial magnets. At the Earth's surface, the field strength ranges from about 25 to 65 microteslas (0.25 to 0.65 gauss). In contrast, a small neodymium magnet can have a field strength of about 1 tesla at its surface, which is thousands of times stronger than Earth's field. However, what makes Earth's field remarkable is its vast scale, extending tens of thousands of kilometers into space.