21 : Capacitance

Question 1

What is a capacitor

Answer 1

an electrical component that stores charge on two seperate metal plates with an insulator placed in between called a dielectric to prevent charge travelling through the gap

Question 2

charging a capacitor

Answer 2

• plate A attracts electrons from negative terminal of battery
• positive terminal of battery attracts electrons from late B
• electron build on plate A = electrons removed from B creating a p.d across plates
• when p.d aros plates = p.d of source then capacitor is charged and current stops

Question 3

Define Capacitance

Answer 3

the charge stored per unit p.d

Question 4

capacitors in parallel

Answer 4

C=C1+C2
because V=V

Question 5

capacitors in series

Answer 5

1/C = 1/C1 + 1/C2
because Q=Q

Question 6

Area under V/Q graph

Answer 6

work done = energy stored

Question 7

discharging a capacitor

Answer 7

• charge on one plate decreases as it loses electrons and other plate gains
• becomes neutral
• p.d decreases exponentially

Question 8

time constant

Answer 8

• CR
• time taken for p.d to decrease to 1/e of original value

Question 9

capacitors uses

Answer 9

• touchscreen
• smoothing AC
• camera flash
• backup generators

Question 10

relative permittivity

Answer 10

• ratio of the charge stored with dielectric present to when there is no dielectric
• greater permittivity = greater capacitance

Question 11

factors that affect t

Answer 11

• capacitance
• the amount of Q that can be stored by capacitors at any p.d.
• resistance
• affects the current and how quickly it flows thus speed capacitor charges or discharges