Edexcel A Level Physics

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3.12 Potential Difference & Conductor Length

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Potential Difference & Conductor Length

Potential Difference

  • A cell makes one end of the circuit positive and the other negative. This sets up a potential difference across the circuit
  • The potential difference across a component in a circuit is defined as;

energy transferred per unit charge

  • The energy is transferred is from electrical energy into other forms, depending on the component or device being used
  • Potential difference is measured in volts (V) which are equivalent to Joule per coulomb (J C−1)
  • The potential difference of a power supply connected in series is always shared between all the components in the circuit

Potential difference in a circuit, downloadable AS & A Level Physics revision notes

The potential difference is the voltage across each component in a circuit

  • Another description of energy transfer is work done
  • Therefore, potential difference can also be defined as the work done per unit charge


Potential difference equation, downloadable AS & A Level Physics revision notes

Potential difference is the work done per unit charge

Measuring Potential Difference

  •  Potential difference or voltage is measured using a voltmeter
    • A voltmeter is always set up in parallel to the component being measured

Voltmeter in a circuit, downloadable AS & A Level Physics revision notes

Potential difference can be measured by connecting a voltmeter in parallel between two points in a circuit

Conductor Length

  • The equation for resistivity is

R equals fraction numerator rho l over denominator A end fraction

  • Where:
    • R = resistance (Ω)
    • ρ = resistivity (Ω m−1)
    • l = length (m)
    • A = area (m−2)

  • Therefore, as the length of a uniform conductor at constant temperature increases, resistance also increases
  • Voltage and current are linked by Ohm's Law

V space equals space I R

  • Where
    • V = potential difference (V)
    • I = current (A)
    • R = resistance (Ω)
  • Therefore, as R increases, so must potential difference across the wire
    • Potential difference increases uniformly with length

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