Capacitance Flashcards
Capacitance
ratio of charge to potential of a conductor
charge stored per unit pd
Capacitance of a parallel plate capacitor
3 marks
Capacitance= charge/potential
Charge is numerically equal to charge on one plate
Potential is the p.d between the two plates
Capacitor
Device that stores energy
Practical use of a capacitor
used in computers to store energy so that they can gradually release this energy if there is a power failure and save valuable data
Three uses of capacitors in electrical circuits
- smoothing
- storage of charge
- producing electrical oscillations
Describe how a capacitor stores energy
2 marks
- on a capacitor, there is charge seperation.
- energy is released when charges come together
for parallel plate capacitor
Explain why a capacitor stores energy but not charge
3 marks
- charges on plates are equal and opposite
- so no resultant charge
- energy stored because there is charge seperation
To charge a capacitor (4)
- connect to dc
- electrons of power supply move to one plate
- p.d builds
- when pd= emf, charging stops
To discharge a capacitor (2)
- connect plates directly without a power supply
- negative charge moves to positive plate
What is the effect of adding a resistor when discharging a capacitor?
Increased resistance means decreased current
charge flows off capacitor’s plates more slowly
capacitor will take longer to discharge
How to make a capacitor store more energy
Use a supply of higher emf when charging
Capacitance formula
C= Q/V
Capacitance in series
same as resistance in parallel
Capacitance in parallel
same as resistance in series
when capacitors are connected in parallel, they have the same…
voltage
when capacitors are connected in series, they have the same…
charge
area of v-q graph?
Energy stored in a capacitor
work done formula (2)
W= 1/2QV
W= 1/2CV²
Time constant formula
= RC
Time constant def
Measures how long it takes for a capacitor to discharge
formula to find current, charge or pd for a capacitor discharging through a resistor
x=xₒ e^-t/RC
