5.1 What are capacitors

Question 1

What is the equation for capacitance?

Answer 1

c = q/v  
where  
c  = capacitance 
q = charge 
v = pd

Question 2

What is capacitance measured in?

Answer 2

Farads

Question 3

What is the circuit symbol for a capacitor?

Answer 3

two lines of same length with a gap between them

Question 4

What is capacitance ?

Answer 4

amount of charge per unit voltage stored by capacitor

how much charge can be stored per 1V

Question 5

What field is created between two plates of a capacitor?

Answer 5

uniform electric field

Question 6

What is a capacitor?

Answer 6

An electrical component that can store electrical potential energy using an electric field. Two conducting plates separated by an insulating material in the middle

Question 7

What does a capacitor store?

Answer 7

Charge (electrical potential energy in an electric field)

Question 8

How do the plates of the capacitor become charged?

Answer 8

As current starts to flow the charge carriers get deposited on one of the plates (assuming the charge carriers are electrons), the plate becomes negatively charged. The charge carriers are repelled off the plate in the other terminal making the other plate charged.

Question 9

How is pd created between the plates?

Answer 9

Charge carriers cannot move through the gap, so a pd is created and therefore an electric field.

Question 10

How will the strength of the electric field change as we leave the capacitor charging?

Answer 10

• its strength will increase
• until the pd across the gap is equal to the pd of the power supply
• due to the conservation of charge basically, makes sense

Question 11

what are the three factors that impact capacitance

Answer 11

• the size of the plates
• their separation
• the nature of the insulator between them

Question 12

Describe the practical used to determine the capacitance of a capacitor.

Answer 12

We have a series circuit with an variable resistor, ammeter, capacitor, switch and a cell. Also we have a voltmeter around the capacitor. Using a stopclock we record the time it takes the pd to increase by a certain amount each time, while current is kept constant using a variable resistor(same as initial value).

Question 13

How can we work out the capacitance from our results?

Answer 13

By plotting a graph of Q against V. We get Q by multiplying current x time. The gradient should be the capacitance.

Question 14

What type of energy do the capacitors store?

Answer 14

Electric potential energy

Question 15

What happens to capacitance in parallel (of different capacitors)

Answer 15

They are added together.

cT = c1 + c2 + c3……..

Question 16

What happens to capacitance in series?

Answer 16

Capacitors work against each other.

1/ct = 1/c1 + 1/c2………..

Question 17

How can we remember the rules for capacitance in circuits?

Answer 17

Opposite for rules for resistance