Resistance

As given by Ohm's Law Resistance is the ratio of voltage to current in a circuit. Resistance is measured in Ohms, frequently abbreviated as Ω.

Resistance resists electrical flow, just like a steep hill slows a car's speed. If you think of amperage as the weight of a car and resistance as the steepness of the hill, then voltage is the amount of horse-power needed to get up that hill. So the same horse power could get a smaller car up a larger hill than it could a large truck. The behavior of electricity is similar.

1 volt can push 1 amp through 1 ohm of resistance. That same 1 volt can only push 1/2 amp through 2 ohms of resistance. 2 volts would be needed to push that same 1 amp through the 2 ohms of resistance.

Example: Say you have a circuit that is rated as a maximum of 5 volts. What is really happening is that the circuit has a resistance of 50 ohms, and therefore can only take 1/10th of an amp before it burns out. So anything more than 5v would push too much current (amps) through the circuit.