439 Thermodynamic MCQ For All Mechanical Exams

201) For real gases,

  1. a) specific heats vary appreciably with temperature
  2. b) specific heats vary little with pressure
  3. c) both of the mentioned
  4. d) none of the mentioned

Ans-D

202)At constant temperature, (u being the internal energy)

  1. a) u change when v or p changes
  2. b) u does not change when v or p changes
  3. c) u does not change when t changes
  4. d) u always remains constant

Ans-B

203)Characteristic gas constant is given by (here cp=specific heat at constant pressure and cv is the specific heat at constant volume)

  1. a) R=cv – cp
  2. b) R=cp + cv
  3. c) R=cp – cv
  4. d) none of the mentioned

Ans-C

204)The value of cp and cv depend on

  1. a) temperature of the gas
  2. b) ɣ and R
  3. c) pressure of the gas
  4. d) all of the mentioned

Ans-B

205)The maximum and minimum values of ɣ is

  1. a) 1.33, 1
  2. b) 2.00, 1
  3. c) 1.67, 1
  4. d) 1.25, 1

Ans-C

206)Which of the following is true for a polytropic process?

  1. a) p(v^n) is used to describe the process
  2. b) it is not adiabatic
  3. c) it can be reversible
  4. d) all of the mentioned

Ans-D

207)In the equation p(v^n), n is calculated by

  1. a) (logp1 + logp2) / (logv2 + logv1)
  2. b) (logp1 – logp2) / (logv2 – logv1)
  3. c) (logp1 – logp2) / (logv2 + logv1)
  4. d) none of the mentioned

Ans-B

208)Polytropic specific heat is given by cn=cv(ɣ-n)/(1-n) .

  1. a) true
  2. b) false

Ans-A

209)Which of the following is true?

  1. a) for n>ɣ, there will be positive heat transfer and gain in entropy
  2. b) for n<ɣ, there will be negative heat transfer and decrease in entropy
  3. c) both of the mentioned
  4. d) none of the mentioned

Ans-C

210)Which of the following relation is correct?

  1. a) cv = R/(ɣ-1)
  2. b) cp = ɣR/(ɣ-1)
  3. c) ɣ = cp/cv
  4. d) all of the mentioned

Ans-D

211)In a gas compressor,

  1. a) work is done on the gas to raise its pressure
  2. b) there is an appreciable increase in its density
  3. c) both of the mentioned
  4. d) none of the mentioned

Ans-C

212)For ɣ>n>1 and for the same pressure ratio p2/p1, the maximum work is needed for

  1. a) isothermal compression
  2. b) adiabatic compression
  3. c) polytropic compression
  4. d) all need same work

Ans-B

213)For minimum work the intermediate pressure is the _____ of the suction and discharge pressures.

  1. a) arithmetic mean
  2. b) geometric mean
  3. c) sum
  4. d) difference

Ans-B

214)Heat rejected in the intercooler is given by (here cp is the specific heat at constant pressure)

  1. a) cp*(T3-T2)
  2. b) cp*(T3+T2)
  3. c) cp*(T2-T3)
  4. d) none of the mentioned

Ans-C

215)If there are N stages of compression, then the pressure ratio in each stage is

  1. a) p2/p1 = (discharge pressure/suction pressure)^(1/N)
  2. b) p2/p1 = (suction pressure/discharge pressure)^(1/N)
  3. c) p2/p1 = (discharge pressure/suction pressure)^N
  4. d) p2/p1 = (suction pressure/discharge pressure)^N

Ans-A

216)The isothermal efficiency of a compressor is given by

  1. a) p1*v1/ total work of compression
  2. b) p1*v1*ln(p2/p1) / total work of compression
  3. c) total work of compression / p1*v1*ln(p2/p1)
  4. d) total work of compression / p1*v1

Ans-B

217)The ratio of the actual volume of gas taken into cylinder during suction stroke to the piston displacement volume is called the volumetric efficiency.

  1. a) true
  2. b) false

Ans-A

218)Clearance(C) is defined as

  1. a) (piston displacement per cycle / clearance volume )^n
  2. b) piston displacement per cycle / clearance volume
  3. c) clearance volume / piston displacement per cycle
  4. d) (clearance volume / piston displacement per cycle)^n

Ans-C

219)The volumetric efficiency is given by

  1. a) 1-C+C(p2/p1)^(1/n)
  2. b) 1+C-C(p2/p1)^(1/n)
  3. c) 1+C+C(p2/p1)^(1/n)
  4. d) 1-C-C(p2/p1)^(1/n)

Ans-B

220)Volumetric efficiency decreases as the clearance _____ and as the pressure _____

  1. a) decreases, increases
  2. b) increases, decreases
  3. c) decreases, decreases
  4. d) increases, increases

Ans-D

221)Compressors are built with the maximum clearance.

  1. a) true
  2. b) false

Ans-B

222)For a fixed clearance, as the pressure ratio is increased, the volumetric efficiency of a compressor

  1. a) decreases
  2. b) increases
  3. c) remains constant
  4. d) none of the mentioned

Ans-A

223)A pure substance which exists in a single phase has ____ independent variables.

  1. a) zero
  2. b) one
  3. c) two
  4. d) three

Ans-C

224)Maxwell’s equations consists of ____ equations.

  1. a) four
  2. b) three
  3. c) two
  4. d) one

Ans-A

225)Which of the following is not a Maxwell equation?

  1. a) (∂T/∂V) = -(∂p/∂S)
  2. b) (∂T/∂p) = -(∂V/∂S)
  3. c) (∂p/∂T) = (∂S/∂V)
  4. d) (∂V/∂T) = -(∂S/∂p)

Ans-B

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