Question

D04 and D05. An air-filled parallel plate capacitor has circular parallel plates each of radius R = 100 cm. They are separated by a distance d = 0.100 cm. The capacitor is part of an RC circuit as shown in the circuit diagram below. The EMF of the battery is 50 V. R = 100 ΜΩ (1ΜΩ = 10 Ω). The switch is initially open and the capacitor is uncharged. 100 MS2 EMF so V SWIT CH DO4. (i) What is the time-constant of this circuit? (ii) If the switch is closed, derive an expression for the magnitude of the E field between the capacitor plates at some time t (ignore edge effects).

Answer 1

Capacitance, c = E_0 A/d Area of the plantes, A = pi R^2 pi times (100)^2 cm^2 pi times (100)^2 times 10^-9 m^2 pi m^2. d = 0.100m = 0.001 m c = E_0 A/d = 2.781 times 10^-8 F R = 100M Ohm. 10^8 Ohm. Therefore Time constant of the circuit, T = RC = (10^8 times 2.781 times 10^- 8) 2.781 sec (Ans)