Question

A uniform electric field $E = 2 \times 10^3\, N\, C^{-1}$ is acting along the positive $x$-axis. The flux of this field through a square of $10 \,cm$ on a side whose plane is parallel to the $yz$ plane is

• A. $20 \,N\, C^{-1}\, m^2$
• B. $30 \,N\, C^{-1}\, m^2$
• C. $10 \,N\, C^{-1}\, m^2$
• D. $40 \,N\, C^{-1}\, m^2$

Answer 1

Answer: (A)

Here, $E = 2 \times 10^3\, N\, C^{-1}$ is along $+ x$-axis Surface area, $s = (10\, cm)^2 = 10^2 \times 10^{-4}\, m^2 = 10^{-2}\, m^2$
when plane is parallel to $yz$ plane, $\theta = 0^°$
So $\phi=ES\,cos\theta=2\times10^{3}\times10^{-2}\,cos\,0^{°}=N\,C^{-1}\,m^{2}$