# Question 6 (a) Define electric flux. Write its S.I. units. (b) How is the field directed if (i) the sheet is positively charged, (ii) negatively charged? (Delhi 2012)

Solution,
a)
Total number of electric field lines passing through a given area is called electric flux.
$\varphi =\int \stackrel{\to }{E}.\stackrel{\to }{dS}=ES\mathrm{cos}\left(\theta \right)$
where, $\theta$ is the angle between the electric field lines and the area vector.
The SI unit of electric flux is Nm2/C.
b)
(i). If the sheet is positively charged, the electric field is directed perpendicular and away from the plate surface.
(ii). If the sheet is negatively charged, the electric field is directed perpendicular and towards the plate surface.

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