Potential divider

A potential divider consists of an resistor, R, in series with a resistor and a power supply.

Calculate:

• the current

• the p.d. across each resistor

• Calculating the current:

  • Total resistance =
  • ->

• Calculating the p.d. across each resistor:

  • :
  • :
  • Check that they add back up to the EMF:

What if one of the resistors is variable?

• If one resistor can change, the ratio of resistances will change.
• This will then change the p.d. across each resistor.
• This is useful in sensors - e.g. an LDR or thermistor.

A potential divider consists of an resistor, R, in series with a thermistor and a power supply. Calculate the p.d. across at each temperature.

The thermistor has a resistance of at 20°C and at 100°C.

• At 20°C:
• At 100°C: