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
