# 6.1 Capacitance

What does a capacitor do?
Store charge.
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What makes up a capacitor?
Two parallel metal plates (conductors) insulated from each other.
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How does a capacitor work?
When the plates are connected to a battery, electrons from the negative terminal flow onto one plate. Electrons leave the other plate and return to the positive battery terminal.
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Why do the plates have an equal and opposite charge?
An equal number of electrons are gained by one plate from the negative terminal, as flow back to the positive terminal from the other plate.
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What equipment is needed to charge a capacitor at constant current?
A variable resistor, a switch, a microammeter and a cell in series with the capacitor.
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How is Q calculated from this experiment?
Using Q=It, t is the time after the switch is closed and I is the current recorded.
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How do we measure the capacitor p.d?
Using a high resistance voltmeter connected in parallel with the capacitor.
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How to investigate how the capacitor p.d changes with time?
Use variable resistor to keep the current constant, and measure voltmeter reading at certain times.
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What does a graph showing stored charge against p.d look like?
A straight line through the origin.
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What is the gradient of the Q/V graph?
The capacitance.
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What is the definition of capacitance?
The stored charge per unit pd.
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What is the unit of capacitance?
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Some examples of uses of capacitors?
Back-up power supplies, circuits that smooth out unwanted variations in voltage, circuits which switch on and off repeatedly.
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## Other cards in this set

### Card 2

#### Front

What makes up a capacitor?

#### Back

Two parallel metal plates (conductors) insulated from each other.

### Card 3

#### Front

How does a capacitor work?

#### Back ### Card 4

#### Front

Why do the plates have an equal and opposite charge?

#### Back ### Card 5

#### Front

What equipment is needed to charge a capacitor at constant current?

#### Back 