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Electric & Magnetic Flux, Density & Field Intensity Formulas

Electric Flux, Magnetic Flux, Electric Density, Magnetic Density, Electric Intensity and Magnetic Intensity Formulas & Equations

Electric & Magnetic Flux, Density & Field Intensity Formulas

Electric Flux Formula:

Electric flux is the electric field lines passing through an area A. It’s a vector quantity.


ΦE = EA cosθ


  • Φ= Electric flux
  • E = Electric field
  • A = Area of the surface
  • θ = Angle between E and A

Non Uniform Electric Filed

dΦE = E dA

Electric flux for a closed Gaussian surface

ΦE = ∯s E dA = Q/ε0


  • Φ= Electric flux
  • E = Electric field
  • A = Area of the surface
  • Q = electric charge inside the surfaces of A
  • ε0 = permittivity of free space (also known as universal or electric constant which is equal to ε0 ≈ 8.854 187 817… x 10−12 F·m−1.)

The above equations is one of the four Maxwell’s equations also known as Gauss’ law related to an electric field.

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Electric Flux Density Formula:

The electric flux per unit area is called the electric flux density.

D = ΦE /A

Other forms of equations for electric flux density are as follow:

D = εE = q/4πr2

E = q/4πεr2

E = q/4πεrε0r2

D = εrε0E


  • D = Density
  • ΦE = Electric flux
  • A = Area

It is a scalar quantity and the unit is C/m2 i.e surface charge density “σ”.

Electric Field Intensity Formula:

Force per unit charge is known as electric field intensity.

E = F/Q


  • E = Electric Field Intensity
  • F = Force
  • Q = Electric Charge

The electric filed strength in volt per meter formula is as follow:

ε = e/d

Magnetic Flux Formula:

The number of magnetic lines passing through area A is known as Magnetic flux.

Φb = BA cosθ


  • Φb = magnetic flux
  • B = Magnetic field
  • A = area
  • θ = angle between B and A

It is a vector quantity and the general form of magnetic flux can be calculated by using the following equation:

ΦB = ∫∫A B dA

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Magnetic Flux Density Formula:

The magnetic flux per unit area is called magnetic flux density in Tesla (webers per metre2) and it is a vector quantity.

B = Φ/A


  • B = Magnetic Flux Density
  • Φ = Magnetic Flux
  • A = Area

Magnetic Field Intensity Formula:

Magnetic field strength or magnetic field intensity can be calculated by using the following equations

H = I/(2πr)


H = Fm/le    …   Ampere per meter.


H = B/μ0 – M


  • H is the magnetic field intensity or magnetic field strength
  • B is the flux density
  • M is the magnetization
  • μ0 is the permittivity
  • l is the length
  • F is the MMF (Magnetic motive force)

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