## 2008-10-09

### Resistance

This is another important property that can be measured in an electrical system. This resistance, which is measured in the SI unit called ohm, Ω.

Resistance is a term that describes the opposition experienced by the electrons as they flow in a conductor. All materials naturally contain some resistance to the flow of current.

A water analogy can be used to understand the concept of resistance. Consider a water hose that is partially plugged with sand. The sand will slow down the flow of water in the hose. We can say that the plugged hose has more resistance to water flow than an unplugged hose. If we want to get more water out of the hose, we would need to increase the water pressure.

The same is true with electricity. Materials with low resistance let electricity flow easily. Materials with higher resistance require more voltage to make a similar current flow.

R = V/I
R = resistance
V = voltage(potential difference)
I = current

This is actually derived from V = IR

Resistance can be both good and bad. If we are trying to transmit electricity from one place to another through a conductor, resistance is undesirable in the conductor. Resistance causes some of the electrical energy to turn into heat, so some electrical energy is lost along the way.

However, it is resistance that allows us to use electricity for heat and light. The heat that is generated from electric heaters or the light that we get from light bulbs is due to the resistance of the wire. In a light bulb, the current flowing through a resistance filament causes it to become hot and then glows hence giving voluminous ray of light.