The Winner

This simulation shows a simple circuit containing one resistor. In addition there is a voltmeter (parallel to the resistor) and an ammeter (in series with the resistor).

You can select the maximum voltage and maximum amperage values tolerated by the meters by using the pull down boxes. If you see the warning "Maximum exceeded!", you have to choose an adequate measuring range. Resistance (R) and voltage (U) can be changed with the four buttons. On the bottom right, the values of voltage (U) and current (I) are indicated.

Lihat Gambarnya Disini

If you go through this simulation and create a ratio of voltage to current you would find that this ratio is a constant value for any given circuit (only as long as temperature remains constant). This is known as Ohm's law.

This ratio results in the term resistance which is measure in Ohms (Greek letter OMEGA) An Ohm can be broken down into many units but it is usually not worth going any farther than a volt per amp.

Generally speaking, any object that requires electrons to do work as they pass through it can be considered a resistor.

Sumber :http://www.sciencejoywagon.com/physicszone/otherpub/wfendt/ohmslaw.htm
Untuk lebih jelasnya lihat Disini