Physics - Current, Voltage and Resistance

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A few important terms:

  • Current = flow of electric charge round the circuit. Unit = ampere, A
  • Potential Difference (voltage - they're the same thing) = Driving force that pushes the current round. Unit: volt, V
  • Work Done = the energy transferred. Unit = joules, J
  • Resistance = anything within the circuit that slows the flow down. Unit: ohm,Ω

The greater the resistance across a component, the smaller the current that flows

Total charge through a circuit depends on current and time:

  • Current is the rate of flow of charge. 
  • Current = charge / time
  • Current (I) = charge (Q) / time (t)
  • I = Q/t
  • Current (I) is measured in amps (A)
  • Charge (Q) is measured in coulombs (C)
  • Time (t) is measured in seconds (s)
  • More charge passes around the circuit when a bigger current flows

Potentical Difference (Voltage)

Potential difference (or voltage) is the work done (the energy transferred, measured in joules, J) per coulomb of charge that passes between two points in a circuit. The forumla for this is - P.D. = Work Done/Charge. So the potentical difference is the amount of energy transferred by the electrical component (eg light and heat energy by a bulb) per unit of charge.


A voltmeter measures the potential difference between two points. 

  • A battery transfers energy to the charge as it passes (the push that moves the charge along)
  • Components transfer energy away from the charge (to use a lamp eg)
  • Voltage of a battery shows how much work the battery will do to the charge that passes through it (how big of a push it


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