Potential Dividers, EMF and Internal Resistance

What is a potential divider?

2 or more resistors connected in series with each other and a source of pd.

What are potential dividers used for?

To supply a constant or variable potential difference from a power supply.

What range of potential difference can a potential divider supply?

From 0V to the value of the source.

State the potential divider equation.

I = Vs / R1 + R2

If R1 is significantly greater than R2, what happens to the voltage across R1?

It is close to the supply voltage.

Draw a potential divider circuit.

Define EMF.

Work done to move 1C of charge through the cell.

What are the units for EMF?

J C^-1 or V

State the equation linking EMF, energy and charge.

emf = energy / charge

Define internal resistance.

The loss of potential difference per unit current in the source when it flows through.

State the equation connecting emf and internal resistance.

EMF = I(R + r) = Ir + V

How can you reduce “lost volts” across a battery?

Lower the current.

How do you calculate lost volts?

v = Ir

State the equation linking current, emf, resistance and internal resistance.

I = EMF / R + r