In 1798, Count Rumford observed that the amount of heat produced is proportional to the amount of mechanical work done. Later, Dr. James Prescott Joule of Manchester, established a definite relation between the work done and the heat produced. It was shown that when a certain amount of mechanical work is done, an equivalent amount of heat is always produced.
If W is the amount of mechanical work done and Q is quantity of heat produced, then
where J is a constant of proportionality.
It is known as Joule's constant or Joule's mechanical equivalent of heat.
If Q = 1, then J = W.
Joule's mechanical equivalent of heat may be defined as the amount of work done so as to produce a unit quantity of heat.
