Question

(each plate is a circular disk of diameter 20 cm)

Set up the plate separation at 2 cm

#	d	Electrometer reading (V)	1/V	C=kε0A/d
1	2mm	100	0.01
2	3mm	90	0.011
3	4mm	80	0.0125
4	5mm	70	0.143
5	6mm	60	0.016

2. plot a graph with C along y-axis and 1/V along the x-axis.

3. What is the value of slope and what physical quantity it gives?

Answer 1

here Area A = pi r^2

r = D/2 = 20cm/2 = 10 cm = 0.1 m

A = 3.14 * 0.1^2 = 0.0314^2

and now

for d = 2 mm = 0.002 m ,

C = eoA/d = (8.85*10^-12* 0.0314)/(0.002)

C =138.9 pF

------------------

for d = 3 mm, C =(8.85*10^-12* 0.0314)/(0.003) = 92.63 pF

for d = 4mm, C = (8.85*10^-12* 0.0314)/(0.004) = 69.47 pF

for d = 5 mm, C = (8.85*10^-12* 0.0314)/(0.005) = 55.57 pF

for d= 6 mm, C = (8.85*10^-12* 0.0314)/(0.006) = 46.315 pF

this plot will be linear

and this plot of C vs 1/V gives CV = Constant = charge Q