practical 6 - internal resistance and emf

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Created by
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Cards (5)

  • equipment
    • battery or cell
    • voltmeter
    • ammeter
    • variable resistor
    • switch
  • method
    • set up apparatus
    • open switch and record voltage
    • set variable resistor to maximum value
    • close switch and record voltage and current
    • open switch between readings
    • decrease resistance of variable resistor and repeat obtaining pairs of readings over widest possible range
  • graphs and calculations
    • plot graph of voltage against current and draw line of best fit
    • emf = y-intercept
    • gradient = negative internal resistance
    • ϵ=\epsilon=I(R+r)=I\left(R+r\right)=V+V+Ir  →  V=Ir\ \ \rightarrow\ \ V=−rI+-rI+ϵ\epsilon
  • safety
    • high current can heat up wires which is dangerous
    precautions
    • use another resistor in series
  • improvements
    • only close the switch whilst finding readings
    • prevents internal resistance from changing
    • use new cells because emf and internal resistance changes over a cell's life