The Potential Divider

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Potential Dividers

  • Potential Dividers reduce voltage. Varying the ratio of a pair of resistors changes the output voltage of a circuit.
  • V[out] = V[in] * (R2) / (R1+R2)
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What are Potential Dividers?

  • Two resistors in series that split the potential difference from the spurce between them.
  • One of the resistors is fixed and the other can change resistance (e.g. variable resistor, LDR or thermistor)
  • The varying resistance of one of the resistors then changes the proportion of the potential difference that it uses.This is used to control an output potential difference across one of the resistors.
  • R[total] = R1 + R2
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Rearranged Formulae

  • R2 = V[out] * (R1) / (V[in] - V[out])
  • R1 = R2 * (V[in] - V[out]) / V[out]
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Supplying a Variable PD

  • Instead of having two fixed resistors it can be useful to have a sliding point along a piece of resistance wire or alternatively a sliding contact in a drum formation. This creates a ratio of resistances between the two parts of the resistor
  • V1/V2 = R1/R2
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Sensor Circuits

  • You can use an LDR or thermistor to create sensor circuits based on light or temperature conditions
  • These can be used to directly feed pd to a device (e.g. cooling fan) or to turn a switch on and off on a secondary circuit (a solenoid system)
  • A variable resistor often takes the place of the fixed resistor so that the circuit can be "tuned" (i.e. seting the temperature at which the circuit will turn a fan on and off)
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