3.7.4 Capacitance

Question 1

What is capacitance

Answer 1

Capacitance (of a capacitor) = the charge stored per unit of p.d across the capacitor
C=Q/V

Question 2

What is a capacitor

Answer 2

An electrical component that stores electric energy in the electric field

Question 3

What is the unit of capacitance

Answer 3

Farad

Question 4

What is the relationship between charge and voltage

Answer 4

Directly proportional

Question 5

Describe briefly how capacitance works

Answer 5

The two plates build up equal but opposite amounts of charge.
The charge stops building once the p.d of the capacitor equals the p.d of the power supply.
The charge stays there until there is a way for it to discharge.

Question 6

How is energy stored in a capacitor

Answer 6

As the capacitor increases in charge, it also stores an increasing amount of energy.
This is electric potential energy which can be used during a discharge.
W=VQ

Question 7

What is the energy stored by a capacitor

Answer 7

The amount of energy stored by a capacitor is the amount of work done pushing the charge onto the plate.
W=QV

Question 8

What is the useful energy

Answer 8

Half of the energy will be dissipated

Question 9

what is a dielectric

Answer 9

a material which increases the capacitance of a capacitor
(allows capacitor to store more charge)

Question 10

what does the capacitance of a parallel plate capacitor depend on

Answer 10

distance between plates
area of plates
if there is a dielectric

Question 11

what is the equation showing the relationship between capacitance and what it depends on
(capacitance of a parallel plate)

Answer 11

capacitance = (areapermittivity of free spacepermittivity of dielectric) / distance between the plates