Question

The most usually-studied capacitors is made up of two parallel conducting plates. These are separated by 1.77 mm. What is the capacitance in air if the plate in 17 cm²? What is the charge is a potential difference of 120 V is applied? 

Answer 1

The capacitance of the parallel plate capacitor

$$C=\frac{\epsilon_0A}{d}=\frac{8.85*10^{-12}*17*10^{-4}}{1.77*10^{-3}}\\ =8.5*10^{-12}\:\rm F=8.5\: pF$$

The charge at the capacitor plates

$$q=CV=8.5*10^{-12}*120\\ =1.02*10^{-9}\:\rm C=1.02\: nC$$