Given a uniform electric field E = 5 × 10³ î N/C, find the flux of this field through a square of 10 cm on a side whose plane is parallel to the Y-Z plane. What would be the flux through the same square if the plane makes a 30° angle with the X-axis?

E = 4 × 10³ î (N/C)
Flux = E ⋅ S = EScosθ
S is the area through which electric field lines cross
When plane is parallel to Y-Z plane then θ = 0
here S = a × a = a² a = 5cm
Flux = ES = 4 × 10³ × (5 × 10⁻² )² = 4 × 10³ × 25 × 10⁻⁴ = 10
When plane makes angle 30 degree with X axis then perpendicular to plane makes angle 60 degree to X axis
hence θ = 60°
Flux = ES = 4 × 10³ × (5 × 10⁻²)² × cos60° = 4 × 10³ × 25 × 10⁻⁴ × ½ = 5