Question

two plane sheets of charge densities +ve sigma and -ve sigma are kept .what are the electric field intensities at point a and b?

Answer 1

at point A,

electric field intensity due to left plate on A = $\frac{\sigma}{2\epsilon_0}$ away from the plate.

electric field intensity due to right plate on A = $\frac{\sigma}{2\epsilon_0}$ towards the plate.

so, net electric field at A = $\frac{\sigma}{2\epsilon_0}+\frac{\sigma}{2\epsilon_0}$

= $\frac{\sigma}{\epsilon_0}$

similarly, at point B,

electric field due to left plate on B = $\frac{\sigma}{2\epsilon_0}$ away from the plate.

electric field due to right plate on B = $\frac{\sigma}{2\epsilon_0}$ toward the plate.

so, net electric field at B = $\frac{\sigma}{2\epsilon_0}-\frac{\sigma}{2\epsilon_0}=0$