Absolute Zero on celsius scale

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Discussion Overview

The discussion revolves around determining the location of absolute zero on the Celsius scale using a Carnot cycle problem involving heat input and rejection at specified temperatures. The scope includes theoretical and mathematical reasoning related to thermodynamics.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • Arya presents a problem involving a Carnot cycle where 20 KJ is added at 100 degrees Celsius and 14.6 KJ is rejected at 0 degrees Celsius, seeking to find absolute zero on the Celsius scale.
  • Mapes prompts Arya to consider the relationships between extracted work, rejected heat, and the temperatures of the hot and cold reservoirs in the Carnot cycle.
  • Arya explains the Carnot cycle relationships, stating that the ratio of heat input to temperature of the source equals the ratio of rejected heat to the temperature of the sink.
  • A participant outlines the efficiency of the Carnot cycle and provides the formula relating efficiency to the temperatures of the reservoirs, suggesting Arya derive the solution from this point.
  • Mapes notes that temperatures should be referenced from an absolute zero variable rather than fixed Celsius values, indicating a need to solve for this variable.
  • Arya acknowledges the misunderstanding regarding absolute zero as a variable and indicates that the problem has been resolved after this clarification.

Areas of Agreement / Disagreement

Participants generally agree on the relationships within the Carnot cycle, but there is an initial misunderstanding regarding the treatment of absolute zero as a variable. The discussion appears to resolve this misunderstanding without further contention.

Contextual Notes

The discussion does not explicitly resolve the mathematical steps needed to derive the location of absolute zero, as it focuses on clarifying the approach rather than providing a final answer.

arya_jsr
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Hi ,
Please help me to solve following problem.

If 20 KJ are added to a carnot cycle at a temperature 100 degree Celsius and 14.6 KJ are rejected at 0 degree Celsius,determine the location of absolute zero on celsius scale?

Ans -270.16 C

Please tell me how to solve it

Thanks in advance.
Regards
Arya
 
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Hi Arya, welcome to PF. What do you know about the Carnot cycle relationships between extracted work, rejected heat, and the temperatures of the hot and cold reservoirs?
 
Mapes said:
Hi Arya, welcome to PF. What do you know about the Carnot cycle relationships between extracted work, rejected heat, and the temperatures of the hot and cold reservoirs?

Hi Mapes,
In carnot cycle suppose Q1 is given as heat input and T1 is temperature of source,and
Q2 is rejected heat at temperature T2(Temperature of sink),then (Q1/T1)=(Q2/T2) and if W is the work done by reversible cyclic heat engine then Q1=Q2+W.
Now please tell me how to solve this problem
regards
Arya
 
The Efficiency is defined as:

E=\frac{Q_h-Q_c}{Q_h}

Qh is the heat extracted and Qc is the head expelled.

Then, we can derive using basic thermodynamic laws that the efficiency of the Carnot Cycle is given by:

E=1-\frac{T_c}{T_h}

Where Th is the temperature of the hot reservoir and Tc is the temperature of the cold reservoir. Can you figure it out from here?
 
arya_jsr said:
Hi Mapes,
In carnot cycle suppose Q1 is given as heat input and T1 is temperature of source,and
Q2 is rejected heat at temperature T2(Temperature of sink),then (Q1/T1)=(Q2/T2) and if W is the work done by reversible cyclic heat engine then Q1=Q2+W.

Looks good. Now T_1 and T_2 are measured from the absolute zero of the system, which is a variable for this problem. So you can't just use 100°C and 0°C; rather, you need to reference these to the absolute zero variable. Then solve the equation for this variable.
 
Thanks My Friend Mapes,
I got it ,it solved my problem.Actually i was not taking absolute zero as a variable .Now i have solved it.Thanks
regards
Arya
 

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