Magnetic Field - Definition, Formula, Diagram, Properties, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:31 PM IST

If you put a small magnet near a paper clip, the clips start attracting towards the magnets even if the magnet is not touching the clips. This happens due to the magnetic field. A magnetic field is the invisible region around a magnet where its force can be felt. It has both strength and direction, represented by magnetic field lines, which show the path a magnetic force follows. Let's explore this concept in detail in the below article.

This Story also Contains

What is a Magnetic field?
What are Magnetic Field Lines?
Magnetic field Strength
How is Magnetic Field Created?
Properties of Magnetic Field Lines

Magnetic Field - Definition, Formula, Diagram, Properties, FAQs

What is a Magnetic field?

Magnetic fields are defined as the area around a magnet where the influence of the magnet can be felt. It has both magnitude and direction, and the magnetic field, as well as its field and direction, are represented by magnetic field lines.

S.I. Unit of Magnetic field is Tesla (T). and it is represented by B.

Magnetic field

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What are Magnetic Field Lines?

Magnetic field lines are imaginary lines that encircle a magnet. The density of a field's line indicates its magnitude. The magnetic field is strongest around the Poles of a magnet and weakens as it goes away from the poles.

Experiment to Observe Magnetic Field

A simple experiment can help to clarify the concept of magnetic field lines. Fix a sheet of white paper to a table and centre it with a bar magnet. Iron filings should be sprinkled around the magnet. Tap the table gently. It can be seen that the iron filings align in a certain pattern that represents the magnet's field. When these patterns are well examined, it is possible to see that iron filings collect around the poles, but the concentration is lower in the region away from the poles.

Magnetic field Strength

Magnetic field strength, also known as magnetic intensity is the portion of a material's magnetic field that is caused by an external current and is not intrinsic to the material itself. It is denoted by the vector H and is measured in amperes per metre.

How is Magnetic Field Created?

A magnetic field can be produced not just by a magnet, but also by a moving charge or electric current. We are all aware that matter is made up of small bits known as atoms. An atom's nucleus is made up of protons and neutrons, with electrons orbiting around it. The magnetic field is created by the spinning and circling of protons and neutrons or the nucleus of an atom. The magnetic field's direction is determined by the orbit and spin directions.

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Properties of Magnetic Field Lines

1. Magnetic field lines never cross each other.

2. It follows the path with the least resistance between the opposing magnetic poles. A bar magnet's magnetic lines of force travel in closed loops from one pole to the other.

3. The density of the field lines decreases as they pass from the higher permeability region to the lower permeability region.

4. Lines travel from the south pole to the north pole within a material magnetic field, while in the air, they flow from the north pole to the south pole.

5. The density of the magnetic field varies with distance from the pole. Their density reduces as one moves away from the pole.

6. Because it has both magnitude and direction, the magnetic field is a vector quantity.

Properties of Earth's Magnetic Field

1. The magnetic field of the Earth is uniform.

2. The magnetic field strength at the earth's surface is about 10^-4 Tesla.

3. The earth's magnetic field extends up to a height of 5 times the radius of the earth.

Frequently Asked Questions (FAQs)

1. Why do the magnetic field lines matter?

For the following reasons, magnetic flow lines are important:

1. The magnetic field lines shall be lines in a magnetic field, whose tangent shall give direction at every location of the field, and their density shall give field magnitude.

2. They mark the magnetic field direction.

3. Intensity of the magnetic field varies on the number of lines.

4. The lines at the poles are higher, thus the magnetic field at the poles is more powerful.

5. The force of the magnetic field depends on the number of magnetic field lines in a certain location.

2. Where is the strongest magnetic field?

The magnetic field is stronger in the poles because the field lines are most concentrated there. Field lines also demonstrate what happens to the magnetic fields of two magnets when they attract or repel one another.

3. Does space contain magnetic fields?

Yes, space contains magnetic fields. The spiral arms of the Milky Way seem, on the basis of investigations of several pulsars and the polarisation of their radio waves, a very big organised magnetic field. Magnetic fields were observed in interstellar dust clouds. The fields are increased as these clouds collapse.

4. What impacts the magnetic field strength of electromagnets?

Factors that affect the strength of an electromagnet's magnetic field: Factors that influence electromagnet strength are the nature of the core material, the current strength of the core, the number of turns on the centre, and the shape and size of the core.

5. How does shape influence the magnetic field?

A magnet's form has an impact on its force. If there is a pointing end of a magnet, it is stronger than the remainder of the magnet. It's because the form impacts the magnetic energy distribution in the region it occupies.

6. What is the formula for magnetic field strength?

The magnetic field strength (B) is given by the formula B = F / (qv), where F is the magnetic force experienced by a charged particle, q is the charge of the particle, and v is its velocity perpendicular to the magnetic field.

7. What are the units of magnetic field strength?

The SI unit of magnetic field strength is the tesla (T). One tesla is equal to one newton of force per ampere-meter of current. Another commonly used unit is the gauss (G), where 1 tesla = 10,000 gauss.

8. What is magnetic flux?

Magnetic flux is a measure of the total magnetic field passing through a given area. It's calculated by multiplying the magnetic field strength by the area it passes through, considering the angle between the field and the area's normal vector.

9. How does the strength of a magnetic field vary with distance?

The strength of a magnetic field decreases with distance from its source. For a simple bar magnet, the field strength decreases inversely with the cube of the distance (1/r³) from the magnet's center.

10. How do magnetic fields affect charged particles in motion?

Magnetic fields exert a force on moving charged particles that is perpendicular to both the particle's velocity and the magnetic field direction. This force causes the particle to move in a circular or helical path, depending on its initial velocity relative to the field.

11. How is a magnetic field represented in diagrams?

Magnetic fields are typically represented by lines called magnetic field lines. These lines show the direction of the magnetic force at any point in space. The closer the lines are together, the stronger the magnetic field in that region.

12. What is the difference between magnetic field lines and electric field lines?

Magnetic field lines form closed loops, while electric field lines start on positive charges and end on negative charges. Also, magnetic field lines are always perpendicular to the force on a moving charge, while electric field lines are parallel to the force on a stationary charge.

13. How does Earth's magnetic field differ from a bar magnet's field?

Earth's magnetic field is similar to that of a bar magnet, but it's not perfectly aligned with Earth's rotational axis. The magnetic north pole is actually near the geographic south pole, and vice versa. Earth's field is also more complex and less uniform than a simple bar magnet's field due to various factors like the planet's core composition and movements.

14. What is the right-hand rule in magnetism?

The right-hand rule is a method used to determine the direction of a magnetic field around a current-carrying wire. Point your thumb in the direction of the current, and your fingers will curl in the direction of the magnetic field lines.

15. What is the Hall effect?

The Hall effect is the production of a voltage difference across an electrical conductor when a magnetic field is applied perpendicular to the flow of current. This effect is used in sensors to measure magnetic field strength and in some types of electric motors.

16. What is a magnetic field?

A magnetic field is a region around a magnet or a moving electric charge where magnetic forces can be detected. It's an invisible force field that exerts influence on other magnetic materials or moving charged particles within its range.

17. Can magnetic fields exist without electric currents?

While moving electric charges (currents) create magnetic fields, magnetic fields can also exist without electric currents. Permanent magnets, for example, create magnetic fields due to the alignment of their atomic magnetic moments, not due to macroscopic currents.

18. How do ferromagnetic materials affect magnetic fields?

Ferromagnetic materials, like iron, can concentrate and strengthen magnetic fields. When placed in a magnetic field, they become magnetized and can significantly increase the overall field strength in their vicinity.

19. What is magnetic permeability?

Magnetic permeability is a measure of how easily a material can be magnetized in response to an external magnetic field. It's the ratio of the magnetic field in a material to the external field causing it. Materials with high permeability, like iron, are more easily magnetized than those with low permeability, like air.

20. How do magnetic fields interact with electric fields?

Magnetic and electric fields can interact to produce electromagnetic fields. A changing magnetic field can induce an electric field, and a changing electric field can induce a magnetic field. This interplay is the basis for electromagnetic waves, including light.

21. What is magnetic moment?

Magnetic moment is a measure of the strength and orientation of a magnet or current loop. It represents the torque that the magnet or loop would experience in a uniform magnetic field. The magnetic moment of an atom arises from the orbital motion and spin of its electrons.

22. What is magnetic hysteresis?

Magnetic hysteresis is the tendency of a magnetic material to retain its magnetization even after the external magnetic field is removed. This property is crucial in creating permanent magnets and is also responsible for energy losses in transformers and other electromagnetic devices.

23. What is the difference between hard and soft magnetic materials?

Hard magnetic materials, like those used in permanent magnets, retain their magnetization strongly and are difficult to demagnetize. Soft magnetic materials, like iron cores in transformers, are easily magnetized and demagnetized. The difference lies in their magnetic coercivity, which is much higher for hard magnetic materials.

24. What is magnetic reconnection?

Magnetic reconnection is a process where opposing magnetic field lines break and rejoin, releasing magnetic energy as kinetic energy and heat. This phenomenon is important in solar physics, explaining solar flares and coronal mass ejections, and in fusion research for understanding plasma behavior.

25. How do magnetic fields interact with superconducting materials?

Superconductors exhibit perfect diamagnetism below their critical temperature, expelling all magnetic fields (Meissner effect). However, some superconductors (Type II) allow partial penetration of magnetic fields above a certain strength, forming quantized magnetic vortices. This behavior is crucial for high-field superconducting magnets used in MRI machines and particle accelerators.

26. How do magnetic fields affect the properties of materials at the quantum level?

At the quantum level, magnetic fields can alter the energy levels of electrons in atoms and molecules (Zeeman effect), affecting their spectroscopic properties. They can also influence the spin states of particles, which is important in quantum computing and spintronics.

27. How do magnetic fields contribute to the formation and structure of galaxies?

Magnetic fields play a crucial role in galaxy formation and evolution. They influence the dynamics of interstellar gas, affect star formation processes, and contribute to the transport of cosmic rays. Large-scale galactic magnetic fields are thought to be generated and maintained by dynamo processes, similar to those in stars and planets.

28. What is the quantum Hall effect and how does it relate to magnetic fields?

The quantum Hall effect occurs in two-dimensional electron systems subjected to low temperatures and strong magnetic fields. It manifests as the quantization of the Hall conductance, revealing fundamental aspects of quantum mechanics. This effect has led to a precise definition of electrical resistance and has applications in metrology and quantum computing.

29. What is magnetic resonance and how is it used in spectroscopy?

Magnetic resonance occurs when the magnetic moments of atoms or nuclei in a material align with an external magnetic field and are then perturbed by an electromagnetic wave of the right frequency. This principle is used in Nuclear Magnetic Resonance (NMR) spectroscopy to study molecular structures and in Electron Paramagnetic Resonance (EPR) spectroscopy to study materials with unpaired electrons.

30. What is magnetic anisotropy and why is it important in data storage?

Magnetic anisotropy refers to the directional dependence of a material's magnetic properties. In data storage, materials with high magnetic anisotropy are desirable because they can maintain their magnetization in a specific direction, even in small volumes. This property is crucial for creating stable, high-density magnetic storage media, such as hard drives and magnetic tapes.

31. What is magnetic reconnection and why is it important in space physics?

Magnetic reconnection is a process where oppositely directed magnetic field lines break and rejoin, releasing magnetic energy as kinetic energy and heat. This phenomenon is crucial in space physics, driving solar flares, coronal mass ejections, and interactions between the solar wind and Earth's magnetosphere. It's also important in fusion research and astrophysical processes like accretion disks around black holes.

32. How do diamagnetic materials respond to magnetic fields?

Diamagnetic materials, like water or copper, slightly repel magnetic fields. When placed in a magnetic field, they develop a weak magnetic field in the opposite direction, resulting in a repulsive force. This effect is usually very weak compared to paramagnetism or ferromagnetism.

33. How do superconductors interact with magnetic fields?

Superconductors exhibit perfect diamagnetism, known as the Meissner effect. They completely expel magnetic fields from their interior, causing the field lines to bend around them. This property allows for phenomena like magnetic levitation.

34. What is the Biot-Savart law?

The Biot-Savart law describes the magnetic field generated by an electric current. It states that the magnetic field at any point is proportional to the current and inversely proportional to the square of the distance from the current element. This law is fundamental in calculating magnetic fields from complex current distributions.

35. How does the shape of a conductor affect the magnetic field it produces?

The shape of a current-carrying conductor greatly influences the magnetic field it produces. For example, a straight wire produces circular field lines around it, while a circular loop produces a field similar to that of a bar magnet. Solenoids (helical coils) can produce strong, uniform fields inside them.

36. What is magnetic susceptibility?

Magnetic susceptibility is a measure of how much a material will become magnetized in response to an applied magnetic field. It's related to, but distinct from, magnetic permeability. Materials with positive susceptibility are attracted to magnetic fields (paramagnetic), while those with negative susceptibility are repelled (diamagnetic).

37. How do magnetic fields in MRI machines work?

MRI (Magnetic Resonance Imaging) machines use strong magnetic fields to align the nuclear magnetization of hydrogen atoms in water in the body. Radio frequency pulses are then used to alter this alignment, and the resulting signal is used to create detailed images of the body's internal structures.

38. What is the relationship between electricity and magnetism?

Electricity and magnetism are two aspects of the same fundamental force: electromagnetism. Moving electric charges create magnetic fields, and changing magnetic fields induce electric currents. This intimate relationship is described by Maxwell's equations and forms the basis of many modern technologies.

39. How do magnetic fields affect compass needles?

A compass needle is a small, magnetized piece of metal that aligns itself with the Earth's magnetic field. When brought near another magnetic field, the needle will reorient to align with the resultant field, which is the vector sum of Earth's field and the local field.

40. What is magnetic shielding?

Magnetic shielding is the practice of reducing or blocking magnetic fields in a specific area. It's often achieved using materials with high magnetic permeability, like mu-metal, which redirect magnetic field lines around the shielded region. This is important in protecting sensitive electronic equipment and in creating controlled magnetic environments.

41. How do magnetic fields contribute to the auroras?

Auroras (like the Northern and Southern Lights) occur when charged particles from the Sun are guided by Earth's magnetic field towards the poles. These particles collide with atoms in the upper atmosphere, exciting them and causing them to emit light, creating the spectacular auroral displays.

42. How do magnetic fields affect the behavior of plasma?

Magnetic fields strongly influence plasma behavior because plasma consists of charged particles. They can confine, shape, and accelerate plasma. This interaction is crucial in fusion research, where strong magnetic fields are used to contain extremely hot plasma, and in astrophysics to explain phenomena like solar flares and cosmic jets.

43. What is the role of magnetic fields in particle accelerators?

In particle accelerators, magnetic fields are used to steer and focus beams of charged particles. Dipole magnets bend the particle beam to keep it in a circular path, while quadrupole magnets focus the beam. The precise control of these magnetic fields allows scientists to accelerate particles to extremely high energies for collision experiments.

44. What is the magnetocaloric effect?

The magnetocaloric effect is a phenomenon where certain materials change temperature when exposed to a changing magnetic field. This effect is reversible and is being explored for applications in magnetic refrigeration, potentially offering a more energy-efficient and environmentally friendly alternative to conventional refrigeration methods.

45. How do magnetic fields in neutron stars differ from those on Earth?

Neutron stars have incredibly strong magnetic fields, typically billions of times stronger than Earth's. These fields are so intense that they can affect the behavior of matter and light in extreme ways, such as causing vacuum birefringence (where the vacuum itself becomes birefringent) and influencing the emission of X-rays and radio waves from the star.

46. What is magnetic levitation and how does it work?

Magnetic levitation (maglev) is the suspension of an object using magnetic fields to counteract gravity. It can be achieved through electromagnetic suspension (using electromagnets to attract or repel), electrodynamic suspension (using induced currents in conductors), or using superconductors. This technology is used in high-speed trains, frictionless bearings, and some types of wind turbines.

47. How do magnetic fields affect the behavior of light?

While magnetic fields don't directly affect light propagation in vacuum, they can influence light indirectly through their effects on matter. The Faraday effect, for instance, causes the rotation of the plane of polarization of light passing through certain materials in a magnetic field. In extremely strong fields, like those around neutron stars, magnetic fields can affect light propagation directly through quantum electrodynamic effects.

48. How do magnetic fields in the Sun influence space weather?

The Sun's magnetic field is key to solar activity and space weather. Solar flares, coronal mass ejections, and solar wind are all driven by the Sun's complex magnetic field dynamics. These phenomena can affect Earth's magnetosphere, potentially disrupting satellite operations, power grids, and radio communications.

49. What is a magnetic monopole and why haven't we found one?

A magnetic monopole is a hypothetical particle that would be a magnet with only one pole (north or south). Unlike electric charges, which can be isolated as positive or negative, magnetic poles have always been observed to come in pairs. Despite extensive searches, no magnetic monopoles have been definitively detected, though some theories predict their existence.

50. How do magnetic fields affect chemical reactions?

Magnetic fields can influence chemical reactions, particularly those involving radical pairs or transition metal complexes. They can affect the spin states of electrons, potentially altering reaction rates and product distributions. This field of study, known as magnetochemistry, has implications for understanding certain biological processes and developing new chemical technologies.

51. What is the role of magnetic fields in fusion reactors?

In fusion reactors, powerful magnetic fields are used to confine and control the extremely hot plasma required for fusion reactions. These fields prevent the plasma from touching the reactor walls (which would cool it and damage the reactor) and help to compress and heat the plasma. The most common designs, tokamaks and stellarators, use complex arrangements of magnetic fields to achieve stable plasma confinement.

52. 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, is thought to involve specialized proteins (cryptochromes) in the animals' eyes or magnetic particles in their brains. It allows them to sense direction, potentially helping in long-distance migrations and homing behaviors.

53. How do magnetic fields interact with cosmic rays?

Magnetic fields in space, from planetary to galactic scales, strongly influence the paths of cosmic rays (high-energy charged particles from space). They can trap, deflect, or accelerate these particles. Earth's magnetic field, for instance, shields us from many cosmic rays, while interstellar magnetic fields affect the distribution of cosmic rays throughout the galaxy.

54. What is the magnetohydrodynamic dynamo effect?

The magnetohydrodynamic dynamo effect is a process by which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field. This effect is believed to be responsible for generating and maintaining the magnetic fields of planets, stars, and galaxies. It involves the complex interplay between fluid motions and electromagnetic fields.

55. How do magnetic fields contribute to the formation of stars?

Magnetic fields play a crucial role in star formation. They can support molecular clouds against gravitational collapse, regulate the accretion of material onto forming stars, and drive outflows and jets from young stellar objects. The interplay between gravity, turbulence, and magnetic fields is key to understanding the star formation process and the initial mass function of stars.