Capacitance

Question 1

What is capacitance?

Answer 1

Capacitance is the charge stored on one plate per unit potential difference between the plates

Question 2

Potential difference

Answer 2

The energy lost per unit charge by charges passing through a component

Question 3

What is 1 Farad

Answer 3

This is the capacitance of a capacitor in which 1 coulomb of charge causes a prospective of 1 volt.

Question 4

Unit of capacitance?

Answer 4

Farad (F)

Question 5

When is a capacitor said to be fully charged?

Answer 5

A capacitor is fully charged when the potential difference across the capacitor is equal to the emf of the supply.

Question 6

Equation for charge on a capacitor

Answer 6

Q = VC

Question 7

Formula for work done in charging up the capacitor (or energy stored by the capacitor)

Answer 7

W = ¹/₂QV
OR
W = ¹/₂CV²    (Wis proportional to V²)
OR
W = ¹/₂Q² / C

Question 8

Equation for capacitors in parallel

Answer 8

C(total) = C₁ + C₂ + C₃ + …

NB: the pd across the capacitor is the same. The total charge of the capacitors is equal to the sum of the charges.

Question 9

Formula for capacitors in series

Answer 9

1/C(total) = 1/C₁ + 1/C₂ + 1/C₃ + …

NB: each capacitor stores the same charge

Question 10

Formula for capacitance of an isolated body

Answer 10

C = 4πε₀r