Capacitance Flashcards
What is a capacitor?
an electrical component that stores charge on two separate metallic plates. An insulator is placed between the plates to prevent charge travelling through.
Define capacitance:
the charge stored per unit potential difference across the plates
What is the equation of capacitance?
charge/ voltage
In a capacitor how does one of the plates gain a positive charge?
when connected to dc supply there is a brief current as the power supply draws electrons from one plate to another
What is the conservation of charge in terms of the plates?
the charges of the plates are equal and opposite
When does the current stop flowing through the plates?
when the potential difference between the plates equals the EMF of the power supply
How do you calculate capacitance in series?
1/total C = 1/c1 + 1/c2 + 1/c3 etc
How do you calculate capacitance in parallel?
total C = c1 + c2 + c3 etc
Why must work be done by the power supply?
to deposit negatively charged electrons onto the negatively charged plate as like charges repel (same applies to remove electrons from positive plate)
What does the area under a voltage charge graph represent in terms of capacitance?
work done in charging up the capacitor
How can a capacitor be discharged after being charged?
disconnecting the power supply and connecting another electrical component
What happens to the electrons once a capacitor has been disconnected in order to discharge?
the electrons on negative plate no longer have EMF, repel each other, flow round the circuit dissipating electric energy as heat in the resistor
What happens to potential difference, charge and current once the charges of the plates are equal?
all equal 0
What does the time constant of discharging depend on?
capacitance and resistance
What does a higher current cause on the plates?
charge on plates to fall to 0 faster
