Electrical resistance and conductance
Resistance, measured in ohms (symbolized by the Greek letter omega - Ω), is a measure of the opposition to current flow in an electrical circuit.
When an electron moves through a conductor like a metal wire, is when an electric current would flow. Colliding of different moving ions in the metal makes it harder for current to flow which is what causes resistance.
The longer a wire is, the more resistance there is because of the amount of collisions within being more as they pass; this means that the relationship between the two are proportional.
On the other hand, the thinner a wire is, the more resistance. This is because of the space of the passing ions being less meaning the collisions increase. That makes them inversely proportional.
As Resistance increases, current decreases making them inversely proportional.
Calculation
Resistance can be calculated by measuring current via an ammeter and potential difference via a voltmeter and using Ohm’s law.
- V = I x R
or
- Volts = amperes x ohms
Or
- Potential difference = current x resistance
Which can be re-arranged to calculate current:
- R = V/I
Electrical Resistance And Conductance Media
A 75 Ω resistor, as identified by its electronic color code (violet–green–black–gold–red). An ohmmeter could be used to verify this value.
The current–voltage characteristics of four devices: Two resistors, a diode, and a battery. The horizontal axis is voltage drop, the vertical axis is current. Ohm's law is satisfied when the graph is a straight line through the origin. Therefore, the two resistors are ohmic, but the diode and battery are not.
A piece of resistive material with electrical contacts on both ends.
- SanwaSMs
Running current through a material with resistance creates heat, in a phenomenon called Joule heating. In this picture, a cartridge heater, warmed by Joule heating, is glowing red hot.
