Unit 4 edexcel physics 

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  • Created by: Shivani
  • Created on: 22-01-12 11:21
Preview of Capacitors

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When you apply a potential difference to the plates of the capacitor they
become charged and as a result there is an electric field between them.
Q is proportional to V
Q= CV: where C is the constant and it is called capacitance
Capacitance is measured in Farads
Measuring the capacitance of a capacitor
Measuring capacitance involves measuring Q and V
To measure the potential difference is easy use a voltmeter.
Charge is difficult to measure because it is the charge that moves from one
plate to another.
Charge is equal to area under a current- time graph, therefore if the current is
constant then charge=It
To keep the current constants use a rheostat. Record the initial current on the
micro-ammeter and then gradually decreases the resistance of the rheostat to
maintain a constant voltage.
Energy stored in a capacitor
Capacitors store energy.
W=1/2CV^2 or W=1/2QV
Exponential Charge
Exponential growth is when something gets larger by the same amount each
Exponential decay is when something gets smaller by the same fraction each

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When a capacitor discharges the rate of flow of charge is proportional to the
charge remaining
The rate at which a capacitor discharges gets slower as the charge remaining
on the capacitor gets smaller
RC is the time constant, the larger this value the longer it takes to discharge a
capacitor or for a nucleus to decay.…read more


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