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A capacitor consists of two closely spaced metal circular conductors each with 1

ID: 1282755 • Letter: A

Question

A capacitor consists of two closely spaced metal circular conductors each with 10 cm radius and are separated by 1 mm. The capacitor is charge by 10 V battery.

1- What the capacitance of the capacitor?

2- What is charge on each plate of the capacitor

3- If the battery disconnected and then the distance between the two plates increased to 2 mm:

a) What is the voltage between the two plates of the capacitor

b) What is the charge on each plate

4- Repeat part 3 assuming that the battery remains connected between the two plates. What is the charge on each plate

Explanation / Answer

1) C = A*epsilon/d

= 3.14*0.1^2*8.854*10^-12/1*10^-3

= 0.278*10^-9 or 0.278 nF

2) Q = C*V

= 0.278*10^-9*10

= 2.78*10^-9 C or 2.78 nC


3) charge remains same but capacitance becomes half.


a) V' = 2*V = 2*10 = 20 volts

b) Q' = Q = 2.78 nC


4) now V remains same and capacitance becomes half.

a) V' = V = 10 volts

b) Q' = Q/2 = 2.78/2 = 1.39 nC