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 $10cm$ 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 +x axis
Surface area, $s={\left(10cm\right)}^2={10}^2\times {10}^{-4}{m}^2={10}^{-2}{m}^2$
when plane is parallel to yz plane $\theta =0^o$
So,$\varphi =Es\cos \theta =2\times {10}^3\times {10}^{-2}\cos 0^o=20N{C}^{-1}{m}^2$