A large plane charge sheet having surface charge density σ=2.0×10−6 Cm−2 lies in the x-y plane. Find the flux of the electric field through a circular area of radius 1 cm lying completely in the region where x, y, z are all positive and with its normal making an angle of 60∘ with the z-axis. (Given that the field due to infinite charged sheet is σ2ϵ0 where σ = surface charge density. Also note that it is perpendicular to the sheet and is constant for all points from the sheet.)
Now it is given that field is constant but area vector makes some angle with the direction of →E field. You clearly know that in such cases there is a simplified notation as.
The normal to the x-y plane is the z axis and the electric field will be along the z axis. Now from the question, the angle between →E and →A is 600.
So, ϕ=→E→A cos 600