21 : Capacitance Flashcards
1
Q
What is a capacitor
A
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
2
Q
charging a capacitor
A
- 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
3
Q
Define Capacitance
A
the charge stored per unit p.d
4
Q
capacitors in parallel
A
C=C1+C2
because V=V
5
Q
capacitors in series
A
1/C = 1/C1 + 1/C2
because Q=Q
6
Q
Area under V/Q graph
A
work done = energy stored
7
Q
discharging a capacitor
A
- charge on one plate decreases as it loses electrons and other plate gains
- becomes neutral
- p.d decreases exponentially
8
Q
time constant
A
- CR
- time taken for p.d to decrease to 1/e of original value
9
Q
capacitors uses
A
- touchscreen
- smoothing AC
- camera flash
- backup generators
10
Q
relative permittivity
A
- ratio of the charge stored with dielectric present to when there is no dielectric
- greater permittivity = greater capacitance
11
Q
factors that affect t
A
- 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