# capacitance

HideShow resource information
• Created by: syaqub18
• Created on: 22-04-15 18:23
what is capacitance?
the capacitance of an object is the amount of charge it is able to store per unit potential difference
1 of 14
what can a capacitor do?
store electrical charge
2 of 14
what is a capacitor made up of?
two electric conducting plates separated by an electric insulator (dielectric)
3 of 14
what is the circuit symbol for a capacitor?
two parallel lines
4 of 14
how does a capacitor work?
when connected to a dc current power source, charge builds up on its plates, one become negative and one becomes positive, separated by dielectric so charge cant move
5 of 14
what can capacitors be used for?
camera flash, camera battery charges the capacitor, when a picture is taken, the capacitor discharges to flash instantly, can be used to smooth out voltage as capacitor absorbs peaks and fills in the troughs
6 of 14
how does a capacitor store enegry?
because like charges repel and the charges on either side of plate are being forced together against their will. this requires energy from the power source and stored as electric potential energy
7 of 14
which way do the electrons flow from the supply and what effect does this have on the plate?
from the negative terminal and negative charge builds up on the plate
8 of 14
what happens to the opposite plate?
electrons flow from the opposite side making it positive as the electrons are repelled by the negatively charged plate and the electrons repelled are attracted to the positive terminal of the supply
9 of 14
why is the charge equal and opposite?
because the same number of electrons are repelled from the positively charged plate as are built up on the negative
10 of 14
what happens to the current as charge builds up on the plates?
electrostatic repulsion makes it harder and harder for electrons to be deposited, when the p.d across the capacitor is equal to the p.d of the supply the current falls to zero
11 of 14
what happens when you charge through a fixed resistor?
p.d across capacitor is zero at first so no p.d opposing current, p.d of source causes a high current, as capacitor charges the p.d across resistor decreases as p.d across the capacitor increases this causes current to drop
12 of 14
what happens when you discharge through a fixed resistor?
to discharge you remove the source and then reconnect, charged capacitor discharges to the connected resistor, p.d causes a current to flow, current flows in opposite direction from charging current, capacitor is discharged when p.d and current =0
13 of 14
what is the time constant?
RC (where R is resistance of the circuit and C is the capacitance) also is the time taken for Q0 to fall to 37% for a discharging capacitor or the time taken for charging capacitor to rise to 63% of Q0
14 of 14

## Other cards in this set

### Card 2

#### Front

what can a capacitor do?

#### Back

store electrical charge

### Card 3

#### Front

what is a capacitor made up of?

### Card 4

#### Front

what is the circuit symbol for a capacitor?

### Card 5

#### Front

how does a capacitor work?