The discussion revolves around heat transfer in a closed system involving a gas and a moving piston, with specific focus on the implications of applying the First Law of Thermodynamics. Participants are trying to understand the significance of a conducting rod maintained at a constant temperature while heat flows through it.
Several participants have provided insights into the relationship between heat flow, internal energy, and work done on the gas. Some have clarified the assumptions necessary for solving the problem, while others express confusion about the implications of the piston’s movement and its effect on pressure and heat transfer.
Participants note the absence of a figure referenced in the original problem statement, which may affect their understanding. There is also discussion about neglecting heat loss from the system, which raises questions about the assumptions underlying the problem.
sir sorry for that,now i have edited it.mfb said:
thank you for replying sir,but isn't it already given the temperature of the gas is constant 300k.Anyway the internal energy of the gas is constant but how is work done on the gas equal to the rate of heat flow through the rod?Chestermiller said:
All your answers are correct.vijayram said:
sir,why should the rod remove heat from the gas?we don't know how the piston is moving,we can say,piston is moving because of some external heat or if piston is moved physically,heat can escape out of the system.Chestermiller said:
What do the words "Neglect any kind of heat loss from the system (other than through the rod)" mean to you? (Italics are mine for clarification)vijayram said:
Does it mean the heat escaped from the cylinder moves to the rod and heats it?i thought about this but i couldn't be sure?sir but,does how the piston is moved make any significance here?like heating the piston or physically moving it?Chestermiller said:
It flows through the rod at a constant rate from the gas to the cold reservoir. The rod temperature profile does not change with time.vijayram said:
The implication of the problem statement is that the piston is being physically moved.
Thank you very much sir but if the piston is moved by a heater,how would the scenario change?Chestermiller said:
Why don't you solve the problem as stated already? I did, and I obtained one of the choices they offered.vijayram said:
sir i solved the problem and got k/100R as the answer,but i have one more additional doubt,the piston is massless so net force on the piston should be zero or external pressure should be equal to internal pressure,or internal pressure should be equal to atmospheric pressure,but the pressure obtained using gas laws is different as temperature is constant.So isn't this a contradiction,how to explain it sir?Chestermiller said:
External pressure is slightly higher than internal pressure for a reversible compression, and the ideal gas law can be applied even if the temperature is constant. So I don't see any contradictions. The pressure is changing during the compression.vijayram said:
but the piston is massless so according to Newton's law f=ma,m=0 so net external force should be equal to zero.Chestermiller said:
ohvijayram said:
yes i think the same sir,so atmospheric pressure is not equal to internal pressure of the gas and it could be found only through the gas laws.Am i right sir?mfb said:
The net force is essentially zero. The external pressure essentially matches the gas pressure for a reversible compression. As long as the piston moves, however slowly, work is being done on the gas. It may take a long time, however.vijayram said:
but sir,external pressure is constant and is equal to 1 pascal but internal pressure changes with the position of the piston.And the numbers didn't match sir.Could it be like this sir?when the external agent is also taken into account,it comphensates,and the piston cannot move on it's own.Chestermiller said:
Who says that the external force is constant.? I can apply whatever external force I desire manually, and the gas will have to respond. The force I apply does not have to be constant. And it can be over and above the atmospheric pressure (which, incidentally, is 100000 pascals, not 1 pascal).vijayram said:
mfb said:
yes sir understood it clearly,and yes it is 1lakh pascal,but what if the scenario is changed and the piston is heated by a heater?Chestermiller said:
