• Joule’s experiment (1840-1849) to investigate the equivalence of heat and work.

• Prior to Joule, heat was considered to be a invisible fluid known as caloric and flows from a body of higher caloric to one with a lower caloric.

• Caloric theory of heat

• Joule’s experiment laid the foundation of the first law of thermodynamics.

Joule’s experiment

• Work, W1-2 done on the system can be measured by the fall of the weight.

• The system temperature rises as work is done on the system.

• Let the insulation now be removed.

• The system reaches its initial state by heat transfer across the system boundaries.

• Therefore the work done is proportional to the heat transfer.

• The constant of proportionality is the Joule’s equivalent.