capacitors

Question 1

what is a capacitor

Answer 1

a capacitor is a gap on a circuit with space for charge on the plates. it stores charge and therefore energy

Question 2

process of charging a capacitor

Answer 2

electrons from the lower plate repel electrons from the upper plate, which then move to the positive terminal of the supply

Question 3

if we measure the charge stored on a capacitor at different potential differences, what does the Q-V graph look like?

Answer 3

straight line through the origin

charge stored on the capacitor is proportional to the potential difference

Question 4

what is gradient of Q-V graph

Answer 4

capacitance of the capacitor

Question 5

how to find energy stored in a capacitor from graph

Answer 5

area under a charge-potential difference graph

Question 6

energy stored in capacitor equation

Answer 6

E=1/2QV
E=1/2CV squared
E=1/2 Q squared/C

Question 7

current-time graph of charging capacitor

Answer 7

begin to charge extremely quickly as lots of electrons are repelled from the plate. This rate will reduce over time.
Starts high on y-axis and ends low on x-axis

Question 8

current-time graph of discharging capacitor

Answer 8

Initially discharges quickly and reduces over time. However, electrons now travelling opposite way around the circuit so negative.

starts low on y-axis and ends at x-axis

Question 9

voltage-time graph of charging capacitor

Answer 9

a capacitor will begin with zero potential difference before charging rapidly, rising to reach the supply voltage, where it will peak

start at origin and end top right corner

Question 10

voltage-time graph of discharging capacitor

Answer 10

a fully charged capacitor will lose potential difference as electrons leave one plate, before returning to neutral with zero potential difference

starts high on y-axis and ends at x-axis (same as charging current-time graph)

Question 11

factors that determine how long it takes a capacitor to fully charge

Answer 11

1. resistance of the circuit

2. capacitance of the capacitor

Question 12

how does resistance affect charging time of a capacitor

Answer 12

a high value resistor will limit the size of the current and, as the current is the rate of flow of charge, it will take longer for the capacitor to become fully charged.

Question 13

how does capacitance affect charging time of a capacitor

Answer 13

a capacitor with a higher capacitance can hold more coulombs of charge per volt, so it will take longer for the charge to fill the capacitor

Question 14

experiment to investigate charging/discharging of a capacitor

Answer 14

position a - charging
position c- discharging
(V and I every 5 seconds)
diagram in notes

Question 15

capacitance equation

Answer 15

C=Q/V