capacitors

  • Created by: argyrou
  • Created on: 30-04-18 17:15
What is the function of a capacitor?
A device designed to store charge
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Define capacitance
the charge stored per unit potential difference
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That is the equation for capacitance
c=Q/V
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what is the unit of capacitance?
Farrads F
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What is the relationship of charge and potential difference when charging a capacitor?
they are proportional
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what are the 2 equations to calculate energy stored in a capacitor?
E=CV²/2 = QV/2
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what is the area under a pd against charge graph?
energy stored by the capacitor
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what is the energy that is stored by the capacitor?
Electric potential energy
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when discharging a capacitor, what happens to the current charge and pd and what is the term for this?
they all decrease when discharging and they decrease exponentially.
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what is the percentage that the charge/current/pd drops down to after 1 time constant?
37%
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What is the exponential equation to find charge when discharging a capacitor?
Q=Q e^(-t/RC)
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what three quantities decrease exponentially when a capacitor is discharging in the form x=x e^(-t/RC)?
current, charge and pd
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How many time constants does it take to discharge a capacitor? (pretty much)
5 (5RC)
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What is the time constant?
RC - the time taken to discharge a capacitor to 0.37 of its initial value
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what happens to voltage and what happens to current once a capacitor is fullt charged?
pd=source pd and current=0
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What quantity has the same exponential graph when charging and discharging?
current
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What does an exponential graph look like when discharging a capacitor?
Q against t graph:
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what does an exponential graph when charging a capacitor look like (ignoring current)?
Q agaisnt t graph:
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what is the equation for charge when charging a capacitor?
Q=Q (1-e^(-t/RC))
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In the exponential equations, what is the value of e^-t/RC when t=0?
1
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in the exponential equations, what is the value of e^-t/RC when t=infinity?
0
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What is a dielectric?
electrically insulating materials that increase the ability of a parallel-plate capacitor to store charge.
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What is relative permativity and what are the 3 different ways of calculating it?
Its the ratio of charge stored with the dielectric to the chaarge stored without the dielectric. =Q/Q =C/C =I/I
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What is the capacitance of an 'empty' (no dielectric) capacitor c ?
(surface area of each plate x permitivity of free space)/spacing between the plates = A /d
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What is the capacitance of a capacitor with a dielecrtic in it?
C=A /d
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What are the 3 ways of getting a larger capacitance?
- make surface area of each plate as large as possible - making plate spacing as small as possible - filling space between plates with dielectric with largest possible relative permitivity
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Other cards in this set

Card 2

Front

Define capacitance

Back

the charge stored per unit potential difference

Card 3

Front

That is the equation for capacitance

Back

Preview of the front of card 3

Card 4

Front

what is the unit of capacitance?

Back

Preview of the front of card 4

Card 5

Front

What is the relationship of charge and potential difference when charging a capacitor?

Back

Preview of the front of card 5
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