I am trying to solve a carnot cycle numerical, where I encountered a concept doubt.
When heat is absorbed from the heat source/higher reservoir during first isothermal expansion, does the temperature of the higher reservoir decrease? or will the temperature of the heat reservoir remain constant throughout the process? Can anyone please clarify?
A heat reservoir is by definition a system which can exchange heat without changing its temperature. From a practical point of view, think about a reservoir as very large compared to the system at hand. Then its change in temperature is negligible.
When heat is absorbed from the hot reservoir then obviously the hot reservoir will loose some of its energy and this loss of energy surely causes decrease in the temperature of the reservoir but this loss of energy is negligible in front of the stored energy of the reservoir and hence the temperature change is much smaller than its actual temperature. So we generally ignore the temperature change in the reservoir.
To understand it take the example of a pond of hot lava ( molten magma). If we take out a bowl of lava from the pond then surely some of the energy and hence the temperature will decrease but it will be negligible in front of the remaining energy. However the internal energy per unit mass will be unaltered.
