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A-Level Physics > Capacitance > Flashcards

Capacitance Flashcards

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1
Q

Describe a capacitor

A

2 conducting plates separated by a dialectric

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2
Q

What is a dielectric?

A

An insulating material

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3
Q

Define capacitance

A

Amount of charge per unit p.d. stored

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4
Q

How much is a pico?

A

10^-12

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5
Q

Why do we use μF?

A

Because the farad is a huge unit

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6
Q

What is permittivity?

A

How hard it is to generate an electric field in a certain material

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7
Q

How do you calculate relative permittivity?

A

ε/ε₀

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8
Q

What is another phrase for relative permittivity?

A

Dielectric constant

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9
Q

What is another phrase for dielectric constant?

A

Relative permittivity

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10
Q

What happens to a polar molecule in the presence of an electric field?

A

It rotates so that the negative end is attracted to the positively-charged plate

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11
Q

What is a dielectric made up of?

A

Lots of polar molecules

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12
Q

How do you introduce an electric field to polar molecules?

A

Apply a charge to the dielectric

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13
Q

What is the area under the graph of charge-pd

A

Energy stored

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14
Q

What is the equation for energy stored in a capacitor?

A

½QV

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15
Q

Describe the shape of a charge-pd graph?

A

Straight line through the origin

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16
Q

Why is the shape of a charge-pd graph a straight line?

A

pd is directly proportional to the charge stored

17
Q

How does current change as you charge a capacitor?

A

Decreases (negative curve)

18
Q

When a capacitor is fully charged, what is the current in the circuit?

A

0

19
Q

What is the potential difference between the plates of a fully-charge capacitor?

A

Large

20
Q

When current is flowing in a circuit with a capacitor, which plate do the electrons flow onto?

A

The one connected to the battery’s negative terminal

making the terminal negatively-charged

21
Q

How does the build-up of negative charge on a plate move electrons in the circuit?

A

Negative charge repels electrons off the plate connected to the positive terminal

22
Q

How do you discharge a capacitor?

A

Remove the power supply and complete the circuit

23
Q

How does current change as you discharge a capacitor?

A

Decreases (negative curve)

24
Q

What are the two factors for time taken to charge/discharge a capacitor?

A

Capacitance, resistance (of circuit)

25
Q

For a capacitor, which formula in the formula book do you substitute V for Q?

A

“capacitor charging”

the first one

26
Q

For a capacitor, which formula in the formula book do you substitute I for Q?

A

“decay of charge”

the second one

27
Q

Define the “time to halve”?

A

Time taken for the charge/current/pd of a discharging capacitor to halve

28
Q

How do you calculate time to halve?

A

ln2 × time constant

A-Level Physics (13 decks)

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