Module on First Law of Thermodynamics

The first five students’ difficulties found in my study, pertained to the first law of thermo-dynamics. The statement of the first law of thermodynamics involves three terms, ∆U, Q and W. The crux in the understanding of the whole law rests on students’ understanding of each of these terms. It is important to note that the internal energy can be changed by Q or W independently. A situation where the change in internal energy comes about by contribution from both Q and W, in my opinion, would be rather difficult for students to grasp. In order to emphasise the independence of these two processes (Q and W), I thought of two simpler processes, namely, adiabatic compression and isothermal compression, in which one of the three terms is zero. The important factor in the activity-module was quantitative representation of different energy terms. The information sheet, explained students, the relation between change in temperature and the change in internal energy, the sign convention of work done and heat flow in compression and expansion processes. I began with adiabatic process, as students were aware that the net heat flow is zero for such a process. In this process, making ∆T not equal to 0, visible to the students, would prove useful in addressing students’ difficulty of not distinguishing between heat and temperature. This change in temperature that is change in internal energy with Q= 0, would help students realise that heat flow and change in internal energy are not the same. In the isothermal compression, students were shown that though ∆T= 0, heat flows from the system to the surrounding. This would reiterate our addressal of students’ difficulties pertaining to not distinguishing between heat and temperature as well as considering heat and internal energy to be equivalent. In adiabatic compression, the external work during compression process in fire syringe was equated to the change in internal energy. This would be useful in dealing with their difficulty of disregarding work done as a mechanism to change the internal energy of the system. In isothermal compression, the same could be shown through the presence of heat flow when the external work is done.


  1. Adiabatic Compression using Fire Syringe

2. Isothermal Compression

3. External Work done as a mechanism to change the internal energy of the system

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