Homework Solution

TP 4-13 alternate - This problem makes more sense if the temperatures are given on the Celsius scale.

Given:

    E_in = 25000 J

    E_out = 12000 J

    T_H = 600 ^oC

    T_C = 300 ^oC

Find:

    Would you be willing to back financially an inventor marketing the device?

Science:

e = (work output/ energy input ) x 100%

e_max = (1 - T_C /T_H) x 100%

where the temperatures must be expressed in kelvins

Solve:

e = (work output/ energy input ) x 100%

e = (12000 J)/(25000 J)) x 100%

e = 48.0%

e_max = (1 - T_C /T_H) x 100%

 T_H = 273 K + 600 K = 873 K

T_C = 273 K + 300 K = 573 K

e_max = (1 - 573 K / 873 K) x 100%

e_max = 34.4%

    Since  e > e_max the device cannot work (violates the Second Law of Thermodynamics).  Don't invest.