3.4

Question 1

What is a capacitor?

Answer 1

a device that stores electrical charge

Question 2

Explain how a capacitor works

Answer 2

A capacitor is a gap in a circuit with two plates with space for charge. When the capacitor is charged, the electrons on one plate repel those on the other plate, creating a positive plate as the repelled electrons move away, towards the supply.

This creates a potential difference between the plates, therefore allowing the storage of charged particles on the plates.

Question 3

What does ‘a capacitor of 1 farad’ mean in terms of charge stored?

Answer 3

it will store 1 coulomb of charge when the potential difference across it is 1 volt

Question 4

Break down the equation

Q = CV

Answer 4

Q - charge (C)
C - capacitance (F)
V - voltage (V)

Question 5

Draw a graph showing the relationship between charge accumulated across a capacitor and the voltage applied

Answer 5

from zero, it increases upwards

Question 6

How do you calculate the energy stored by a capacitor using this graph

Answer 6

calculate the area under the graph

E = 1/2CV

Question 7

Give 3 equations to calculate energy stored in a capacitor

Answer 7

E = 1/2QV

E = 1/2Q^2/C

E = 1/2CV^2

Question 8

What is an RC circuit?

Answer 8

Resistor-capacitor circuit

Question 9

What happens when a charging a capacitor?

Answer 9

When a capacitor charges, the potential difference increases from 0 to the peak across the capacitor. At the same time, the current decreases in the circuit to zero.

Question 10

What happens when discharging a capacitor?

Answer 10

When a capacitor is fully charged, there is enough energy for the elctrons to pass the gap. This causes potential difference across the capacitor to decrease from the peak to zero, while the current of the circuit decrease