Physics - Electricity - 3.3 - internal resistance

What does e.m.f. stand for?

Electromotive force. (E)

What is electromotive force?

The electrical potential energy supplied to each unit of charge that passes through the source.

What is e.m.f (E) measured in?

Volts.

Where can a voltmeter be placed to measure the e.m.f of a source.

Across the terminals of the source.

What is a load resistor?

A component that uses energy and provides resistance to the current.

What is Ohm’s law?

V = IR, voltage across something = current through it x its resistance

What can the e.m.f. also be expressed as?

The total of all the potential differences (voltages) across all the resistors in the circuit, including across the internal resistance.

equation: E = …

E = IR + Ir, E = V + Ir

equation: r =

r = E - V/ I (V is the terminal potential difference (actual voltage))

What happens to the resistance in a circuit when it short circuits?

The only resistance present is the internal resistance.

What is it important to do when choosing a power supply for an application (resistance)?

To match the external resistance of the appliance to the internal resistance of the source.

Why is it important to match the external resistance to the internal resistance?

It maximises the power output.

equation: P = …

I²R

How can the e.m.f. be determined from a graph of current (x axis) against voltage (y axis)?

The y-intercept (when the current = 0).