Capacitors ! Flashcards
Potential difference - time graph.
How does it change with resistance?
Describe for chartering and discharging capacitors.
The greater the resistance the longer the capacitor will take to (fully) charge or discharge.
Charging:
The smaller the resistance the more ‘cornery’ the curve will be where the corner will be closer to max p.d.
Discharging:
The smaller the resistance the steeper the curve becomes, the closer it gets to the origin.
Or the greater the resistance the more of a straight negative line it becomes.
Explain how a discharging p.d - time curve has a constant-ratio property (exponential decay).
V decreases to 0.37 of its initial value after the time constant.
Define the time constant of a capacitor-resistor discharge circuit.
The time constant for the p.d/ current/ charge decreases to 1/e (0.37) of its initial value.
Capacitance is measured in farads. Define the farad.
Farad = 1 coulomb per unit volt.
Voltage against Charge.
What is the gradient.
What is the area under graph.
Gradient = 1/C Area = Work done, Energy
Define capacitance.
Capacitance = Charge / (per unit) Potential Difference.
Describe and explain in terms of the movement of electrons how the potential difference across the capacitor changes.
(EXPLAIN)
Electrons move in (anti)clockwise motion. (- to +)
Charge on plates decrease/ electrons neutralise positive charge.
p.d. Decreases exponentially
A capacitor is discharging.
The capacitor is in series with a resistor.
Where does the initial energy stored in the capacitor is dissipate to?
It dissipates as heat in the resistor and wire.
Explain in terms of movement of electrons how the capacitor plates acquire an equal but opposite charge.
(EXPLAIN)
State direction of electrons.
Electrons deposited on X removed from Y.
An equal number of electrons removed and deposited on plates.
