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

Answer 1

The correct option is A $20N{C}^{-1}{m}^2$

Here, $E=2\times {10}^{3}N{C}^{-1}$ is along + direction x-axis
Surface area, $s=(10cm{)}^2=102\times {10}^{-4}{m}^2={10}^{-2}{m}^2$
When plane is parallel to yz plane, $\theta =0^{\circ }$
So, $\varphi =Escos\theta =2\times 103\times {10}^{-2}cos{0}^{\circ }=20N{C}^{-1}{m}^2$