Electric Flux Formula

Electric Flux

Electric flux formula is obtained by multiplying the electric field and the component of the area perpendicular to the field. It should be noted that electric flux is defined as the number of electric field lines which are passing through a given area in a unit time. Electric flux has SI units of volt metres (V m), or, equivalently, newton metres squared per coulomb (N m2 C1).

The Formula for Electric Flux

\(\begin{array}{l}\phi=E\, A\, Cos\, \theta\end{array} \)


  • \(\begin{array}{l}\phi\end{array} \)
    is the electric flux
  • E is the electric field
  • A is the area, and
  • \(\begin{array}{l}\theta\end{array} \)
    is the angle between a perpendicular vector to the area and the electric field

Solved Examples

Example 1:

Calculate the electric flux on a plane of area 1 m2 on which an electric field of 2 V/m crosses with an angle of 30 degrees.



E = 2 V/m

A = 1m2

θ = 30°

From the formula of electric flux,

\(\begin{array}{l}\phi=E\, A\, Cos\, \theta\end{array} \)
\(\begin{array}{l}\phi=2V/m\times 1m^{2}\times Cos(30°)\end{array} \)


\(\begin{array}{l}\phi=1\;V\;m\end{array} \)

Example 2:

Determine the electric flux of a flat square having an area of 10 m2 is a uniform electric field of 8000 N/C passing perpendicular to it.



E= 8000 N/C

A= 10 m2

θ = 0° (since electric field is passing perpendicularly)


Φ = 8000 × 102 × Cos(0°)

\(\begin{array}{l}\phi=8\times\,10^{5}\,N\,m^{2}/C\end{array} \)

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