Unit of Magnetic Flux - SI Unit and CGS Unit, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 05:00 PM IST

In this article we will talk about the Magnetic flux, Magnetic flux density, Unit of magnetic flux, magnetic flux density.

What is magnetic Flux?

Magnetic Flux is the number of magnetic field lines passing through the given closed area. It is denoted by the symbol φ (Phi). It is given by the equation

ΦB = B.A = B A cosϴ

………1

Where

φB = Magnetic Flux(Weber)

B= Magnetic Field (Tesla)

A =Enclosed Area (m2)

ϴ= Angle at which magnetic field lines passes through the given enclosed surface area.

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1.2 Units of the Magnetic Flux

The SI unit of the Magnetic Flux is Weber (Wb). Weber unit is named after the German physicist Wilhelm Eduard Weber.

The unit of the magnetic flux can be written or expressed in terms of the other units. For example

Wb=kg m2/s2 A

= V.s

=H.A

=T.m2

=J/A

=108Mx

Where s – second, J –Joules, A- Ampere, T- Tesla, Mx- Maxwell, V- Volt, H- Henry,

CGS Unit of Magnetic Flux

This Story also Contains

1.2 Units of the Magnetic Flux
CGS Unit of Magnetic Flux
Flux Units
1.5 What is Magnetic Flux Density?
1.6 Magnetic Flux Density Unit:
1. 7 Uniform Field Case.
,
1.8 (Calculus) General Cases.
1.9 Understanding Magnetic Flux
1.10 Measurement of Magnetic Flux

Unit of Magnetic Flux - SI Unit and CGS Unit, FAQs

The CGS unit of the Magnetic Flux is Maxwell or Abweber (abWb)

Flux Units

Submultiples of Weber (Wb)

Value	SI Symbol	Name
10-1 Wb	dWb	deciweber
10-2 Wb	cWb	centiweber
10-3 Wb	mWb	milliweber
10-6 Wb	µWb	microweber
10-9 Wb	nWb	nanoweber
10-12 Wb	pWb	picoweber
10-15 Wb	fWb	femtoweber
10-18 Wb	aWb	attoweber
10-21 Wb	zWb	zeptoweber
10-24 Wb	yWb	yoctoweber

Multiples of Weber

Value	SI Symbol	Name
101 Wb	daWb	decaweber
102 Wb	hWb	hectoweber
103 Wb	kWb	kiloweber
106 Wb	MWb	megaweber
109 Wb	GWb	gigaweber
1012 Wb	TWb	teraweber
1015 Wb	PWb	petaweber
1018 Wb	EWb	exaweber
1021 Wb	ZWb	zettaweber
1024 Wb	YWb	yottaweber

1.5 What is Magnetic Flux Density?

Magnetic flux density(B) is outlined because the force acting per unit current per unit length on a wire placed at right angles to the magnetic field.

• Units of B is Tesla (T) or Kgs−2A−1Kgs−2A−1

• B is vector amount

B= F/I*l

………2

l=length of wire

F= force acting on the wire

I=current flowing

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1.6 Magnetic Flux Density Unit:

The CGS and SI unit of magnetic flux density

Unit of Magnetic Flux Density
SI unit	Tesla (abbreviated as T)
CGS unit	Gauss (abbreviated as G or Gs)

Magnetic flux gives the measures of the total number of magnetic field lines passing through the given surface are. The area here can be of any size, orientation with respect to the direction of the magnetic field line. SI Unit of the magnetic flux is Weber. It is a vector quantity. It is measure by the equipment called as Fluxmeter.The magnetic flux per unit area is called as the flux density.

Flux Density= Magnetic FluxArea (Weber/ meter2) (Weber per meter square)

………3

SI Unit of the magnetic flux density is then Wb/m2. It is also called as the magnetic induction. Unit of Magnetic induction is Tesla.

Flux Density= Magnetic FluxArea (Tesla)

………4

Figure 1 Magnetic flux thru a floor is biggest while the floor is perpendicular to the magnetic area lines. In general, magnetic flux of a uniform magnetic area thru flat floor of a loop is ΦB=BAcosθ. We write this in vector notation as ΦB=B⋅A We denotes magnetic flux of magnetic area B with the aid of using ΦB. Consider an open flat floor with location A.A. To take orientation of the floor, we introduce location vector AA which has significance AA and course everyday to the floor.

1. 7 Uniform Field Case.

If B is uniform, then flux of this area thru the floor will be

ΦB,uniform=B⋅A.=BAcosθ

,

Fig 2. Uniform Filed Case

Where θ is angle between B and A.

1.8 (Calculus) General Cases.

In the overall case of arbitrary area and arbitrary floor, we smash the floor into small patches of flat areas, and follow Eq. (3) to every patch. Summing over all patches offers us an estimate of the internet flux thru the floor. We can write this manner as a proper sum. ΦB≈∑B⋅ΔA

Fig 3. General Case

n the restrict of infinitesimally small patches, we get the precise flux,

Which we write as a conceptual integral.

ΦB=∫Surface B⋅dA.

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1.9 Understanding Magnetic Flux

Faraday’s high-quality insights lay on locating a easy mathematical relation to give an explanation for the collection of experiments that he performed on electromagnetic induction. Faraday made several contributions to technological know-how and is broadly referred to as the finest experimental scientist of the 19th century. Before we begin appreciating his work, allow us to apprehend the idea of magnetic flux which performs a main element within side the electromagnetic induction. In order to calculate the magnetic flux, we recall the sphere-line photograph of a magnet or the device of magnets, as proven within side the photograph below.

Fig4. Electrical vs. Magnetic Lines

The magnetic flux via a aircraft of the location given via way of means of A this is located in a uniform magnetic subject of importance given via way of means of B is given because the scalar manufactured from the magnetic subject and the location A. Here, the perspective at which the sphere traces by skip via the given floor location is likewise important. If the sphere traces intersect the location at a glancing perspective, this is,

• While the perspective among the magnetic subject vector and the location vector is sort of same to 90ᵒ, then the ensuing flux may be very low.

• When the perspective is same to 0ᵒ, the ensuing flux is maximum.

Mathematically,

ϕB=B.A=BAcosΘ

Where θ is the perspective among vector A and vector B. If the magnetic subject is non-uniform and at unique elements of the floor, the magnetic subject is unique in importance and direction, then the whole magnetic flux via the given floor may be given because the summation of the manufactured from all such location factors and their corresponding magnetic subject. It is apparent from the equation given above that the magnetic flux is a scalar quantity. It has SI unit of Weber (Wb) or tesla meter squared (Tm2)

1.10 Measurement of Magnetic Flux

Measuring magnetic flux The SI unit for magnetic flux is Weber (Wb) or Tesla square meter (Tm2), named after the German physicist Wilhelm Weber. The magnetic flux can be measured with a magnetometer. Suppose a magnetometer probe is moving in an area. 0.6 m2 near a large magnetic sheet and shows a constant measured value of 5 mT. Then the magnetic flux through this area is calculated as (5 × 103 T) ⋅ (0.6 m2) = 0.0030 Wb. Field reading over an area, it would be necessary to find the average reading.

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NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. How much magnetic field outside a solenoid?

It is null because there are no magnetic field lines outside of a solenoid.

2. What does the index finger represent on the ruler of the left hand?

Shows the magnetic field.

3. Why magnetism generated?

When the charge particle such as electrons moves through the filed that generate the magnetism.

4. What is the unit of strength of the magnetic field?

A.m1 is the unit of strength of the magnetic field.

5. Name the devices that work with torque

when a current-carrying conductor is placed in the magnetic field. The devices are:

Galvanometer

Ammeter

Voltmeter

6. What could affect the strength of a magnet?

Factors that can affect the strength of a magnet:

Heat

Radiation

Strong electrical currents in the vicinity of the magnet

Other magnets in the vicinity of the magnet

Neo magnets corrode in environments with high humidity, unless because they have a protective coating.

7. How does magnetic flux behave in a solenoid?

In a solenoid, the magnetic flux is concentrated within the coil. The flux density inside an ideal solenoid is uniform and proportional to the number of turns per unit length and the current. The total flux through the solenoid is the product of this flux density and the cross-sectional area of the solenoid.

8. What is the significance of magnetic flux in MRI machines?

In Magnetic Resonance Imaging (MRI) machines, strong and uniform magnetic flux is crucial for aligning the spins of hydrogen nuclei in the body. The strength and uniformity of this flux directly affect the quality and resolution of the images produced. Typically, MRI machines use superconducting magnets to generate high and stable magnetic flux.

9. What is the significance of magnetic flux in the design of electromagnetic shielding?

Electromagnetic shielding aims to redirect or absorb magnetic flux to protect sensitive equipment or areas from electromagnetic interference. The effectiveness of shielding depends on its ability to provide a low-reluctance path for magnetic flux, often using high-permeability materials. Understanding magnetic flux behavior is crucial for designing effective shields.

10. What is the role of magnetic flux in the operation of a magnetic levitation (maglev) train?

Magnetic levitation trains use controlled magnetic flux to achieve levitation and propulsion. Superconducting magnets or electromagnets on the train interact with conducting plates or coils on the guideway. By precisely controlling the magnetic flux, the train can be levitated and propelled forward without physical contact with the track.

11. How does magnetic flux behave in diamagnetic materials?

Diamagnetic materials slightly repel magnetic fields, reducing the magnetic flux density within the material compared to free space. When placed in a magnetic field, diamagnetic materials generate a small induced magnetic field in the opposite direction, slightly weakening the overall field. This effect is typically very weak except in superconductors.

12. How is magnetic flux calculated?

Magnetic flux (Φ) is calculated by multiplying the magnetic field strength (B) by the area (A) perpendicular to the field:

13. How does Faraday's law relate to magnetic flux?

Faraday's law states that the induced EMF in a circuit is equal to the negative rate of change of magnetic flux through the circuit. Mathematically, EMF = -dΦ/dt, where Φ is the magnetic flux and t is time. This law demonstrates the direct relationship between changing magnetic flux and induced electrical currents.

14. What is flux linkage?

Flux linkage is the total magnetic flux passing through all turns of a coil. It is calculated by multiplying the magnetic flux through a single turn by the number of turns in the coil. The unit of flux linkage is weber-turns or volt-seconds.

15. What is magnetic flux quantization?

Magnetic flux quantization is a quantum mechanical phenomenon where the magnetic flux through a superconducting loop is constrained to be an integer multiple of a fundamental unit called the magnetic flux quantum (Φ₀). This quantum is equal to h/(2e), where h is Planck's constant and e is the elementary charge.

16. What is the significance of magnetic flux in electromagnetic induction?

Magnetic flux is crucial in electromagnetic induction because changes in magnetic flux induce an electromotive force (EMF) in a conductor. This principle, known as Faraday's law of induction, forms the basis for many electrical devices, including generators and transformers.

17. What is the SI unit of magnetic flux?

The SI unit of magnetic flux is the weber (Wb). One weber is equal to one tesla-square meter (T·m²), representing the magnetic flux through a surface of one square meter perpendicular to a uniform magnetic field of one tesla.

18. How are the SI and CGS units of magnetic flux related?

The relationship between the SI unit (weber) and CGS unit (maxwell) of magnetic flux is:

19. Why are there two different unit systems for magnetic flux?

The existence of SI and CGS units stems from historical developments in physics. The CGS system was widely used in the past, especially in electromagnetic theory. The SI system was later introduced to provide a more standardized and coherent set of units across all fields of physics. Both systems are still in use, with SI being more common in modern scientific literature.

20. What is magnetic flux density, and how is it related to magnetic flux?

Magnetic flux density, also known as the magnetic field (B), is the amount of magnetic flux per unit area perpendicular to the field. It is measured in tesla (T) in SI units or gauss (G) in CGS units. The relationship between magnetic flux (Φ) and flux density (B) is Φ = B · A, where A is the area.

21. What is the difference between magnetic flux and magnetic field strength?

Magnetic flux is a measure of the total magnetic field passing through an area, while magnetic field strength (or magnetic flux density) is the intensity of the magnetic field at a point. Flux is a scalar quantity measured in webers or maxwells, while field strength is a vector quantity measured in teslas or gauss.

22. How does magnetic flux relate to the operation of a Hall effect sensor?

Hall effect sensors measure magnetic flux density perpendicular to their surface. When a current-carrying conductor is placed in a magnetic field, the Lorentz force on charge carriers creates a potential difference (Hall voltage) perpendicular to both the current and the magnetic field. This voltage is proportional to the magnetic flux density.

23. How does the permeability of a material affect magnetic flux?

The permeability of a material determines how easily magnetic flux can pass through it. Materials with high permeability, such as ferromagnetic materials, concentrate magnetic flux and increase the flux density. Low permeability materials, like air, allow less flux to pass through. This property is crucial in the design of magnetic circuits and shielding.

24. What is magnetic flux compression?

Magnetic flux compression is a technique used to generate extremely strong magnetic fields. It involves rapidly compressing a magnetic field using explosives or other means, which increases the flux density in a smaller volume. This technique is used in some types of scientific research and pulsed power applications.

25. What is the significance of magnetic flux in the design of magnetic bearings?

Magnetic bearings use controlled magnetic flux to support a rotating shaft without physical contact. By precisely manipulating the magnetic flux distribution, these bearings can provide stable levitation and reduce friction. The design involves careful consideration of magnetic flux paths, saturation effects, and control systems to maintain stable operation.

26. What is the role of magnetic flux in magnetohydrodynamic (MHD) power generation?

In MHD power generation, a conducting fluid (usually a plasma) is passed through a strong magnetic field. The interaction between the fluid's motion and the magnetic flux induces an electric current perpendicular to both the flow and the magnetic field. This principle allows direct conversion of thermal energy to electrical energy without moving parts

27. How does magnetic flux relate to the concept of magnetic monopoles?

Magnetic monopoles, if they exist, would be sources or sinks of magnetic flux, analogous to electric charges for electric fields. However, all observed magnetic fields form closed loops, with no sources or sinks. This is expressed mathematically as the divergence of magnetic flux density being zero (∇ · B = 0), known as Gauss's law for magnetism.

28. How does magnetic flux contribute to the phenomenon of magnetic hysteresis?

Magnetic hysteresis occurs in ferromagnetic materials when the magnetic flux density lags behind changes in the applied magnetic field strength. This phenomenon results in a loop-shaped B-H curve. The area of this hysteresis loop represents energy loss per cycle, which is important in the design of transformers, motors, and magnetic recording media.

29. How does the shape of a surface affect magnetic flux calculations?

The shape of a surface can significantly affect magnetic flux calculations, especially for non-uniform magnetic fields or curved surfaces. For complex shapes, the flux is often calculated by dividing the surface into small elements and summing the flux through each element. In some cases, surface integrals may be necessary for accurate calculations.

30. Can magnetic flux be negative?

Yes, magnetic flux can be negative. The sign of the flux depends on the chosen direction of the surface normal vector. A negative flux indicates that the magnetic field lines are exiting the surface (opposite to the chosen normal direction), while a positive flux means they are entering the surface.

31. How does magnetic flux relate to magnetic dipole moment?

The magnetic dipole moment of a current loop is related to the magnetic flux through the loop. The dipole moment is equal to the product of the current and the area of the loop. When placed in a magnetic field, the torque on the dipole is proportional to the flux through the loop and the sine of the angle between the dipole and the field.

32. How does the concept of magnetic flux apply to electric motors?

In electric motors, magnetic flux is used to generate rotational motion. The interaction between the magnetic flux from permanent magnets or electromagnets and the current-carrying conductors creates a force (Lorentz force) that causes the motor to rotate. The design of motors often involves optimizing the magnetic flux distribution to maximize efficiency and torque.

33. How does magnetic flux contribute to eddy currents?

Eddy currents are induced in conducting materials when they are exposed to changing magnetic flux. These currents flow in closed loops within the material and can cause heating and energy loss. The magnitude of eddy currents depends on the rate of change of magnetic flux and the material's conductivity.

34. What is magnetic flux?

Magnetic flux is a measure of the total magnetic field passing through a given area. It represents the strength and quantity of magnetic field lines penetrating a surface. The concept is crucial in understanding electromagnetic induction and related phenomena.

35. What happens to magnetic flux if the angle between the magnetic field and the surface changes?

The magnetic flux changes with the angle between the magnetic field and the surface normal. It is maximum when the field is perpendicular to the surface (θ = 0°, cos(θ) = 1) and zero when the field is parallel to the surface (θ = 90°, cos(θ) = 0). This relationship is described by Φ = B · A · cos(θ).

36. What does a positive or negative magnetic flux signify?

The sign of magnetic flux indicates the direction of the magnetic field relative to the surface. A positive flux means the magnetic field lines are entering the surface, while a negative flux means they are exiting the surface. The sign is important when considering the direction of induced currents in electromagnetic induction.

37. How does changing the area affect magnetic flux?

Changing the area directly affects the magnetic flux. If the area increases while the magnetic field remains constant, the magnetic flux will increase proportionally. Conversely, decreasing the area will reduce the magnetic flux. This relationship is linear, as seen in the equation Φ = B · A.

38. Can magnetic flux be zero even if there's a magnetic field present?

Yes, magnetic flux can be zero even in the presence of a magnetic field. This occurs when the magnetic field lines are parallel to the surface (perpendicular to the surface normal), resulting in no field lines passing through the surface. In this case, the angle θ is 90°, and cos(90°) = 0, making the flux zero.

39. What is the CGS unit of magnetic flux?

The CGS unit of magnetic flux is the maxwell (Mx). One maxwell is equal to 10^-8 weber. It represents the magnetic flux through a surface of one square centimeter perpendicular to a uniform magnetic field of one gauss.

40. How does magnetic flux relate to the concept of magnetic reconnection?

Magnetic reconnection is a process where magnetic field lines from different magnetic domains are spliced to one another, changing the field topology. This process involves the breaking and reconnecting of magnetic flux lines, often releasing large amounts of energy. It plays a significant role in solar flares, magnetic substorms, and fusion plasma physics.

41. What is magnetic flux emergence in solar physics?

Magnetic flux emergence in solar physics refers to the process where magnetic flux from the Sun's interior rises through the photosphere and into the solar atmosphere. This emergence creates sunspots and active regions on the solar surface. The study of magnetic flux emergence is crucial for understanding solar activity and space weather phenomena.

42. How does magnetic flux relate to Lenz's law?

Lenz's law states that the direction of an induced current is such that it creates a magnetic field that opposes the change in magnetic flux that caused it. This law is a consequence of the conservation of energy and helps explain the negative sign in Faraday's law of induction.

43. What is the role of magnetic flux in transformers?

In transformers, changing magnetic flux is used to transfer electrical energy between two or more circuits. The primary coil creates a changing magnetic flux in the core, which induces a voltage in the secondary coil. The ratio of the number of turns in each coil determines the voltage transformation ratio.

44. What is magnetic flux leakage?

Magnetic flux leakage refers to the magnetic flux that escapes from the intended path in a magnetic circuit. In transformers and motors, flux leakage reduces efficiency and performance. Magnetic flux leakage testing is also a non-destructive testing method used to detect defects in ferromagnetic materials.

45. What is the relationship between magnetic flux and magnetic vector potential?

The magnetic vector potential (A) is related to magnetic flux through the curl operation. The magnetic flux density (B) is the curl of the magnetic vector potential: B = ∇ × A. The magnetic flux through a surface can be calculated using the line integral of A around the boundary of the surface (Stokes' theorem).

46. How does magnetic flux behave in superconductors?

In superconductors, magnetic flux behaves uniquely due to the Meissner effect. Superconductors expel magnetic flux from their interior, creating a state of perfect diamagnetism. However, in type II superconductors, magnetic flux can penetrate in quantized units called flux vortices above a certain critical field strength.

47. What is the role of magnetic flux in particle accelerators?

In particle accelerators, magnetic flux is used to control the path of charged particles. Bending magnets use strong magnetic fields to curve the particle beam's trajectory. Focusing magnets use specially shaped magnetic flux distributions to keep the beam concentrated. The precise control of magnetic flux is essential for achieving high-energy particle collisions.

48. How does magnetic flux contribute to the Earth's magnetosphere?

The Earth's magnetosphere is created by the interaction of the planet's magnetic field with the solar wind. The magnetic flux from Earth's core extends into space, forming a protective bubble that deflects charged particles from the Sun. The distribution and strength of this magnetic flux play a crucial role in shielding the Earth from harmful solar radiation.

49. What is magnetic flux pumping?

Magnetic flux pumping is a technique used to increase the magnetic flux in a superconducting circuit. It involves cyclically applying and removing a magnetic field to a superconductor-normal metal composite structure. This process can be used to magnetize superconducting magnets without using large external power sources.

50. How does magnetic flux contribute to the operation of a fluxgate magnetometer?

Fluxgate magnetometers use the principle of magnetic saturation to measure weak magnetic fields. They contain a core of easily saturated magnetic material. By applying an alternating current, the core is driven in and out of saturation. The presence of an external magnetic flux changes the symmetry of this saturation, which is detected and used to measure the external field strength.

51. What is the relationship between magnetic flux and magnetic reluctance?

Magnetic reluctance is analogous to electrical resistance but for magnetic circuits. It represents the opposition to magnetic flux in a magnetic circuit. The relationship is similar to Ohm's law: Magnetic flux (Φ) = Magnetomotive force (MMF) / Magnetic reluctance (R). Lower reluctance materials allow more magnetic flux for a given MMF.

52. How does magnetic flux contribute to the generation of cosmic rays?

Magnetic flux plays a crucial role in the acceleration of cosmic rays. In astrophysical environments like supernova remnants or active galactic nuclei, charged particles can be accelerated to extremely high energies by interacting with magnetic flux in shock waves or turbulent magnetic fields. The process often involves magnetic reconnection and diffusive shock acceleration.

53. How does magnetic flux relate to the concept of magnetic helicity?

Magnetic helicity is a measure of the twist and linkage of magnetic field lines within a volume. It is related to the magnetic vector potential and magnetic flux density. Magnetic helicity is conserved in ideal magnetohydrodynamics and plays an important role in the study of plasma physics, solar physics, and astrophysical dynamos.