Capacitors Flashcards
What is the basic structure of a capacitor?
Two metallic plates separated by an insulator or ‘dielectric’
How does a capacitor become charged?
When the capacitor is connected to a cell, one cell loses electrons whilst the other one gains electrons. This means that they have equal and opposite charges.
When a capacitor is charged, what happens to the current, charge and p.d in the circuit?
The potential difference becomes equal to the e.m.f of the cell, the current falls to 0 and the net charge over the capacitor = 0.
What is capacitance?
It is the charge stored per unit potential difference across the capacitor.
For capacitors in parallel, what happens to the potential difference, charge and capacitance?
The potential difference across each capacitor is the same, the total charge stored is equal to the sum of the charges and the total capacitance is equal to the sum of the individual capacitances.
For capacitors in series, what happens to the potential difference, charge and capacitance?
The total potential difference is equal to the sum of the potential differences, the charge on each capacitor is the same and the total capacitance is given by 1/C = 1/C1 + 1/C2 + 1/C3 + …
What does the area under a potential difference against charge graph for a capacitor show?
The work done on the charges or the energy stored by the capacitor.
What are the three equations for energy stored in a capacitor?
W = 0.5 x Q x V, W = 0.5 x V^2 x C, W = 0.5 x Q^2 / C
What is the time constant of a capacitor / resistor circuit.
C x R. It is the time taken for the p.d of a discharging capacitor decrease to about 37% of its initial value.
When a capacitor is charging in a capacitor / resistor circuit, what happens to the p.d on the resistor?
The p.d on the resistor decreases as the p.d on the capacitor increases as they must always add up to the initial p.d.
