Module 6.1 - Capacitors

Question 1

What is capacitance measured in?

Answer 1

Farads (F)

Usually in mF or nF

Question 2

As the capacitor charges up, what happens to the potential difference across the capacitor?

Answer 2

Increases

Question 3

As the capacitor charges up, what happens to the potential difference across the resistor?

Answer 3

Decreases

Question 4

As the capacitor charges up, what happens to the circuit current?

Answer 4

Decreases

Question 5

When will no more charge flow in the circuit?

Answer 5

When the p.d. across the capacitor = e.m.f. of the cell

Question 6

Define capacitance

Answer 6

The amount of charge that can be stored per unit potential difference

Question 7

What is the relationship between charge and capacitance?

Answer 7

Directly proportional

Question 8

Describe how to find the capacitance of a capacitor by monitoring the current and p.d. in a circuit

Answer 8

1) Discharge the capacitor using the shorting/flying lead
2) Close the switch and start the stopwatch
3) Use the variable resistor to keep the current constant
4) Record values for p.d. at regular time intervals
5) Calculate the charge stored using Q=It
6) Plot a graph of Q against V and find the gradient (=C)

Question 9

What is the relationship between energy transferred/work done and p.d.?

Answer 9

Work done is directly proportional to p.d. squared

Question 10

Uses of capacitors

Answer 10

Flash in cameras (high current to excite gas)
Backup energy supplies (emergency current)
Pulsed power in nuclear fusion research (large number of high voltage capacitors)