Ohms Law

Electricity has three properties which are described here:

Terminology	Definition
Voltage	This is the "pressure" that electricity exerts. The greater the voltage, the greater the pressure. In a typical home or office environment a nine volt battery is commonly considered to exert little pressure, but an electric wire with 100,000 volts can exert enough pressure to poke a hole through many materials. However, in a laboratory setting nine volts can exert so much pressure as to damage instrumentation. So, the idea of voltage as pressure and what it means intuitively is relative. Note that electricity can exert all the "pressure" it wants to and the thing it exerts against does not necessarily have to move, but when there is movement than that is called Current.
Resistance	Resistance is the difficulty electricity has getting through something. If there is no resistance then electricity moves without difficulty, but if the resistance is large then electricity has a hard time getting from one place to another and may not move at all.
Current	Current is the amount of electricity that actually moves.

Each of the three properties of electricity is measured in its own unit, described here:

Unit	Definition
Volt	Voltage is measured in the unit called Volt.
Ohm	Resistance is measured in the unit called Ohm.
Amperage	Current is measured in the unit called Amperage. The word Amperage is often shortened to Amp.

Ohms law states:

"Voltage equals resistance multiplied by current"

Most of the time the electrical properties are denoted by symbols according to the following:

Symbol	Definition
V	Voltage
R	Resistance
I	Current

So that Ohms Law, in arithmetic notation, is written as:

V = I × R

Notice that if you keep the current (I) at the same value and change the resistance (R) then the voltage (V) must change proportional to resistance. For the purpose of experiments, such as the Rheostat experiment, you apply Ohms Law to change the voltage by changing the resistance. The Temperature experiment also uses Ohms Law because the sensor changes resistance, which in turn changes the voltage of the electricity going through it.