A point charge of 10 nC is placed at the centre of . . .

Question : A point charge of 10 nC is placed at the centre of the Faraday Cage in the shape of cube with surface of 9 cm edge. The number of electric field lines passing through the cube normally will be : 
a) 1.13×10³

b) 1.13×10⁶

c) 8.85×10⁴

d) 9×10¹²

Doubt by Angad 

Solution : 

Charge (q) = 10 nC = 10×10^-9 C = 10^-8 C

Edge of the cube (a) = 9 cm = 9×10^-2 m

According to Gauss Theorem 

The total electric flux or Electric field lines passing normally = q/ɛ₀
= 10^-8/(8.85×10^-12)
= (10¹²×10^-8)/8.85
= 10⁴/8.85
= 0.1129×10⁴
= 1.129×10³
= 1.13×10³ 

^{Hence, a) 1.13×103 would be the correct option.}