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Questions (19-21)
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In this lesson, questions (19-21) have been explained.

Harshit Aggarwal
Cleared UPSC ESE twice with Rank 63 and 90 in mechanical engg. Got 99 percentile in GATE. Cracked ONGC, BHEL,ISRO, SAIL, GAIL successfully

Unacademy user
you r the best .
Thanks a lot Pradeep
3:03 I couldn't controlled myself..
  1. COURSE : Detailed Explanation on Entropy Questions Lesson : Questions -(19-21

  2. About me Graduated from NIT Nagpur in 2008 * Cleared Engineering Services Examination (ESE-UPSC) Exam Got the offer letter from most of the Maharatna and Navratna Companies , Cleared GATE Exam * Rate, Review, Recommend, Share Follow me on Unacademy at: aggarwal

  3. Question 19 An adiabatic vessel contains 2 kg of water at 25 C. By paddle-wheel work transfer, the temperature of water is increased to 30 C. If the specific heat of water is assumed constant at 4.187 kJ/kg K, find the entropy change of the universe.

  4. Solution 19 (AS)u0 303d'lT (AS)sys- |me 298 2 kg 298 K 303 298 303 K (ASuniv (AS)r 0.139340 0.13934 kJ/K

  5. Question 20 A copper rod is of length 1 m and diameter 0.01 m. One end of the rod is at 100 C, and the other at 0 C. The rod is perfectly insulated along its length and the thermal conductivity of copper is 380 W/mK. Calculate the rate of heat transfer along the rod and the rate of entropy production due to irreversibility of this heat transfer.

  6. Solution 20 0.01 m A = 7.854 10-5 m2 373 K K 380 W/m- K 273 K AT A X = 380 7.854 10-5 100 w = 2.9845W At the 373 K end from surrounding Q amount heat is go to the system. So at this end (AS)change373 And at the 273 K and from system Qamount of heat is rejected to the surroundings (ASare 27:3 (AS)univ.= 273-373 univ0.00293 WIK

  7. Question 21 A body of constant heat capacity Cp and at a temperature Ti is put in contact with a reservoir at a higher temperature T. The pressure remains constant while the body comes to equilibrium with the reservoir. Show that the entropy change of the universe is equal to T, -T, T -T, - ln 1+ Prove that entropy change is positive. Given in (1 + x) = x--+ where x<1

  8. Solution 21 Final temperature of the body will be T Let x as T> T ar (AS) body = C (AS) resoier - . Total entropy charge T-T T, (AS) in = Cr(x-ln (1 + x)} x* x x -in PL2 3 45 T-T T - T, x (3-2x) x(5-4x) 20 (AS) univ is +ve