AQA Physics Unit 2

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Circuits

Current:

  • Current is the number of coulombs per second (amps)
  • The strength of an electric current is measured in amps
  • Amps are a measure of how much electric charge is flowing round the circuit 
  • Current flowing in a circuit can be measured using an ammeter
  • Ammeters must be connected in series with the components (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect04.gif)

Current (A) = Charge (C) / Time (s)


Resistance:

  • Electric current flows when electrons flow and collide with atoms in a conductor
  • These collisions make the conductor hot
  • This is called resistance and it makes it harder for current to flow
  • Resistance is measured in ohms

Resistance (ohms) = Voltage (volts) / Current (amps)


Potential Difference:


  • p.d is measured in volts 
  • When two or more cells are connected in series, the total p.d is the sum of both cells
  • p.d across a component in a circuit is measured using a voltmeter 
  • The voltmeter must be connected in parallel with the components
  • The p.d across a device equals the amount of energy changed (in joules) per coulomb of charge passing through it (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect06.gif)

e.g. the voltage across a lamp is 3V. What does this mean? 

  • That 3J per coulomb are passing through the lamp and are converted into electrical energy.

Potential Difference (V) = energy transferred (J) / charge passes (C)


Current : Voltage graphs:


Resistor

The current flowing through a resistor at a constant temperature is directly proportional to the voltage across the resistor.

So, if you double the voltage, the current doubles too.(http://www.bbc.co.uk/schools/gcsebitesize/science/images/aqaaddsci_02.gif)

Filament

Comments

mushi mashi

Thank you very much

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