Electric Charges and Fields Class 12 Physics - Electric Flux

Electric Charges and Fields Class 12 Physics - Electric Flux
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If the area is not perpendicular to the flow of water. In such case the normal of the area makes some angle θ with the flow of water. So, the flux going through the surface of area dS is v dS cos θ, i.e. . where n^ is unit vector in the direction of normal of the area dS.

The same analogy can be applied in case of electric field and so here we call it electric flux.A point to be mentioned here is that, there is no such flow like water in electric field however there are electric lines of force. If we keep a small planar element of area ΔS perpendicular to E at a point, then the number of field lines crossing the area is proportional to E ΔS. Here also if we tilt the area such that the normal makes some angle θ with the field lines, then the number of field lines crossing the area will be smaller and are proportional to E ΔS cos θ. This means, for θ=90°, area element is parallel to field lines and no field lines cross the area.

Here we define the term electric flux Δⲫ of an electric field through a surface ΔS as
Δⲫ = E·ΔS = E ΔS cosθ
Notice here that flux is scalar quantity and the dot product gives scalar quantity.

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