JOULE’S EXPERIMENT TO VALIDATE FIRST LAW OF
THERMODYNAMICS
AIM: -To Study Joule’s Experiment to Validate First Law of Thermodynamics
APPARTUS: - Thermometer, Paddle Wheel, Stirrer, Water Container, Mass, etc
DIAGRAM: -
PROCEDURE: -
Arrangement similar to Joule's experiment is shown in Fig 1.
It consists of a paddle wheel arrangement with the liquid filled in an insulated container.
The work is supplied across the boundary of the system by a falling weight of mass m (W = mg).
The system is formed by the liquid in the container as a closed system. The work input to the system equals to m.g.z.
As a result of work transfer the temperature of liquid rises, which is measured by a thermometer from initial atmospheric temperature t1, to final temperature t2.
The system has undergone a process (1-A-2) as shown in Fig.2. Next the system was kept in contact with the water bath.
While in contact, the heat is transferred from liquid to water bath till the system returns to its original state of pressure and temperature. The heat transfer process is shown by process (2-B-1) in Fig.2.
Thus the closed system has completed a cycle.
With the help of such experiments, Joule concluded that in every case the work input W was always proportional to heat transfer Q from the system at the end of conclusion of a cycle.
RESULT: -
The results of the experiment can be put mathematically as follows:
∫d′ W ∝ ∫d′ Q
or, ∫d′ W ∝ J ∫ d′ Q
Where, J is a constant and called mechanical equivalent of heat.
CONCLUSION: -
Therefore, statement of First Law of Thermodynamics in various forms can be stated as followheat and work is zero mathematically,
∫ (d′ Q – d′ W) =0
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