Question

An electromagnetic wave has an electric field strength of 145 V/m at a point P in space at time t. A parallel-plate capacitor whose plates have area 0.109 m2 has a uniform electric field between its plates with the same energy density as the answer to part a. What is the charge on the capacitor?

I found the Electric density to be 9.30e-8 but I cant find the relation that I could use to calculate charge.

Answer 1

Gauss:
The amount of electric field coming out of a volume is proportional to the charge inside.

In the case of parallel plates
E = sigma/eo
where sigma is the charge per unit plate area
Multiply sigma by the area to get the total charge. It + on one plate, - ont he other of course.