Question

Two extremely large nonconducting horizontal sheets each carry uniform charge density on the surfaces facing each other. The upper sheet carries +5.00 µC/m2. The electric field midway between the sheets is 4.25 × 105 N/C pointing downward. What is the surface charge density on the lower sheet? (ε0 = 8.85 × 10-12 C2/N · m2)

Answer 1

Remember the property of uniformly charged infinitely large surfaces, no matter what distance you are from the sheets, the electric field is the same. Therefore the distance is irrelevant.

Furthermore, if the electric field is pointing down, we can tell that the lower plate has a negative charge density.



These are the tools you will need: \(\large \Phi_\frac{\overrightarrow{E}}{SG} = \oint_\text{cylinder} \overrightarrow{E} \bullet \overrightarrow{dA}=\frac{q}{\epsilon_0}\)