21 : Capacitance Flashcards

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1
Q

What is a capacitor

A

an electrical component that stores charge on two seperate metal plates with an insulator placed in between called a dielectric to prevent charge travelling through the gap

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2
Q

charging a capacitor

A
  • plate A attracts electrons from negative terminal of battery
  • positive terminal of battery attracts electrons from late B
  • electron build on plate A = electrons removed from B creating a p.d across plates
  • when p.d aros plates = p.d of source then capacitor is charged and current stops
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3
Q

Define Capacitance

A

the charge stored per unit p.d

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4
Q

capacitors in parallel

A

C=C1+C2
because V=V

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5
Q

capacitors in series

A

1/C = 1/C1 + 1/C2
because Q=Q

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6
Q

Area under V/Q graph

A

work done = energy stored

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7
Q

discharging a capacitor

A
  • charge on one plate decreases as it loses electrons and other plate gains
  • becomes neutral
  • p.d decreases exponentially
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8
Q

time constant

A
  • CR
  • time taken for p.d to decrease to 1/e of original value
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9
Q

capacitors uses

A
  • touchscreen
  • smoothing AC
  • camera flash
  • backup generators
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10
Q

relative permittivity

A
  • ratio of the charge stored with dielectric present to when there is no dielectric
  • greater permittivity = greater capacitance
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11
Q

factors that affect t

A
  • capacitance
  • the amount of Q that can be stored by capacitors at any p.d.
  • resistance
  • affects the current and how quickly it flows thus speed capacitor charges or discharges
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