The Potential Divider

Potential Divider

A circuit with a voltage source and a couple of resistors in series

What does a potential divider do

Split the potential difference in the ratio of the resistances

Why are potential dividers used

If you need a potential difference lower than the voltage source

Potential Divider equation

V_out = (R₂/R₁+R₂) x V_s

What are potential dividers mainly used for

Calibrating voltmeters

How can the output voltage of a potential divider be varied

Using a variable resistor

How does increasing the resistance of R₁ affect the output voltage of a potential divider

It will decrease

Why are voltmeters calibrated using potential dividers

You can vary the output voltage using a variable resistor and measure if the value on the voltmeter is correct

Explain why voltmeters are mainly used for potential dividers and not other devices

When attached to the resistor, the device will behave like a resistor in parallel, where the total resistance will always be less than R₂ so the output voltage is slightly less. Voltmeters have a high resistance, making the decrease in total resistance negligible

Explain how a light sensor works

The circuit is a potential divider using an LDR. At higher light levels, the resistance will be lower, giving a higher output voltage

Explain how a temperature sensor works

The circuit is a potential divider using an NTC thermistor. As temperature increases, resistance decreases, giving a higher output voltage

Uniform wire

The same cross-sectional area and material throughout

Flying lead

Wire that curves

Explain how the length of a wire affects potential difference across the length

The resistance of a uniform wire is proportional to its length. This means that the potential difference of a wire is proportional to its length

How does increasing the length of a wire affect the potential difference across that wire

Increases

How does a potentiometer work

One variable resistor is used instead of 2 resistors, but a slider acts to separate it into 2. The slider changes the length of the resistor, which changes the output voltage

Potentiometer

Gives a variable voltage