Current, Voltage and Resistance

Resistance is a measure of how much a material tries to stop electricity passing through it.

As the electrons flow along the wire and collide with the metal atoms they make the metal atoms vibrate more, making the metal hot. This is why all electrical devices waste energy as heat.

Resistance is measured in OHMS (Ω).

Current, Voltage and Resistance
Imagine an electron...
Resistance...
Calculating Resistance
Resistance (Ohms) = Voltage (Volts) ÷ Current (Amps)

R = V ÷ I
Simple Example...
A bulb has a current of 0.5 Amps passing through it, and a voltage of 3 Volts across it. Find its resistance.
Electric current is made up of electrons flowing in a conductor. As an electron flows along a wire, it will bump into the atoms that the wire is made of. This makes it harder for the electron to flow - this is called resistance.
Formula Triangle...
To work out the equation for any term, simply cover it up and see what is left...
Your answer, as always needs 4 steps:

1) An equation.
2) The workings out
3) The solution
4) The unit to go with the answer.
Q1) What effect would making the wire longer have on its resistance? Why?
Q2) What about increasing its diameter? Why?
Q3) What effect do you think resistance has on the wire? Think about what must happen to the energy carried by the electrons...
Georg Ohm, German Physicist who discovered resistance...
The symbol for a resistor. They have a fixed/constant resistance that does not change.
The symbol for a variable resistor. They have a resistance that can be changed, which changes how much current flows in a circuit...