Capacitors Flashcards
What is a capacitor?
A circuit component that stores energy by separating charges onto two electrical conductors (plates) with an insulator between them. One plate becomes positively charged and the other becomes negatively charged.
What is capacitance?
The quantity of charge which can be stored per unit potential difference across the plates of the capacitor.
What is a Farad?
The unit op capacitance. It is equivalent to one coulomb per volt.
What happens when a capacitor is connected to a source of e.m.f?
Charge cannot flow between the plates of the capacitor so electrons will be transferred to the negative terminal of one of the plates. This results in a potential difference across the plates of the capacitor. Once the capacitor has been fully charged, no more charge can flow and the potential difference across the capacitor will be equal to the e.m.f of the cell.
What is the total capacitance of capacitors in a series circuit?
C = C1 + C2 + C3…
What is the total capacitance of capacitors in parallel?
1/C = 1/C1 + 1/C2 + 1/C3…
What do the area and gradient of a graph of potential difference against charge represent?
Gradient = Capacitance Area = Work done
What are capacitors used for?
- Flash devices for cameras
- Back-up energy supplies
- Pulsed power in nuclear fission research
What is exponential decay?
When the quantity decreases at a rate that is proportional to the magnitude of the quantity at that time.
What is the time constant?
The time taken for the charge remaining on a capacitor to decrease to 1/e (37%) of its initial value.
What does the graph of potential difference against time of a charging capacitor look like?
It is an upside-down exponential graph.
What do the graphs for discharging capacitors look like (including current, p.d and charge against time)?
They are all exponential l-shaped graphs. Decreasing exponentially over time.
