Chapter 21 - Capacitors Flashcards
When a capacitor is discharged, what would be the potential difference across a resistor connected in series to the capacitor?
The potential difference across the capacitor
What do V-t, I-t and Q-t graphs show for a discharging capacitor?
They all show exponential decay, as such they all have the same shape, which is a downwards curve.
What is the time constant of a capcitor?
It is equal to the product of the capacitance and the resistance of the circuit. It acts as a measurement of how long the exponential decay will take in a discharging capacitor.
The time constant for a discharging capacitor is the time for…
The p.d/current/charge to decrease to e^-1 (37%) of its initial value
What is a capacitor made up of?
Two electric plates connected by wires, separated by a dielectric
How is a capacitor charged?
The charge from one plate is moved round to the other plate. The plate the charge leaves is positively and the plate the charge moves to is negatively charged.
How do you find the total capacitance of capacitors connected in parallel?
The sum of the capacitance of the capacitors
How do you find the total capacitance of capacitors connected in series?
The reciprocal of the sum of the reciprocal of the capacitance of each capacitor
For capacitors connected in series the charge stored…
By each capacitor is the same
What does the area under a p.d charge graph represent?
work done
Why is the energy stored in a capacitor 1/2QV and not QV?
Energy is lost doing work on the electrons against the electrostatic forces repelling the electrons away from each other.
How do the plates of a capacitor affect the capacitance?
Inversely proportional to the distance between the plates
Directly proportional to the overlapping area of the plates
What is capacitance measured in?
Farad (F)
The energy stored in a capacitor is equal to…
The work done on the charges
