Remember that separated charges have the potential to do
work and provide energy.
The work involved in heating a resistor is not very useful,
unless we are making a hotplate; rather it is a byproduct of
restricting the current flow.
Power is measured in units of watts (W), named after James
Watt, the Englishman who invented the steam engine, a device
for producing lots of useful power.
How to Calculate
The power that is released into the resistor as heat
can be calculated as P=VI , where I is the current flowing
through the resistor and V is the voltage across it.
Ohm's law relates
these two quantities, so we can also calculate the power as The power
produced in a resistor raises its temperature and can change its value
or destroy it.
Most resistors are air-cooled and they are made with
different power handling capacity. The most common values are 1/8, 1/4,
1, and 2 watt resistors, and the bigger the wattage rating, the bigger
the resistor physically.
Some high power applications use special water
cooled resistors. Most of the resistors on the RoboBoard are 1/8 watt.