21.1 - 21.6

Question 1

define ‘capacitance’

Answer 1

the charge stored per unit potential difference across a capacitor

Question 2

what is a capacitor

Answer 2

an electrical component in which charge is separated. they’re made of two metallic plates separated by an insulator

Question 3

how does a capacitor store charge?

Answer 3

when connected to a cell a current is formed for a short time but can’t travel between the plates. one plate loses electrons and the other one gains them. they have opposite charges and thus a P.d across them

Question 4

properties of capacitors in parallel

Answer 4

charged stored = sum of charges in each capacitor

total capacitance = sum of individual capacitances

Question 5

properties of capacitors in series

Answer 5

the charge stored in each capacitor is the same

total capacitance: 1/C(total) = 1/C1 + 1/C2

Question 6

what’s exponential decay

Answer 6

when quantities decrease by the same factor in equal amounts of time

Question 7

what’s the time constant

Answer 7

the time taken for the p.d to decrease to 1/e (≈37%) of its initial value when a capacitor discharges through a resistor

Question 8

what happens to the p.d across components in a capacitor-resistor circuit

Answer 8

the capacitor starts to charge so the p.d across it increases, decreasing the p.d across the resistor. when fully charged the p.d across the resistor is 0