Tag: heat engine: second law of thermodynamics

Questions Related to heat engine: second law of thermodynamics

Which of the following is correct for the efficiency of a heat engine:

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. $\eta=\dfrac{W}{Q _1}$

  2. $\eta=\dfrac{W}{Q _2-Q _1}$

  3. $\eta=\dfrac{W}{Q _2}$

  4. $\eta=\dfrac{Q _2}{Q _1}$

Show answer
Correct Option: A
Explanation:

Efficiency of a heat engine is defined as the ratio of net work done per cycle by the working substance ($W$) to the heat absorbed per cycle from the source ($Q _{1}$) ,

          $\eta=\frac{W}{Q _{1}}$ 

Choose the correct options for the following statements :

A) First law of thermodynamics specifies the conditions under which a body can use its heat energy to produce the work.
B) Second law of thermodynamics states that heat always flows from hot body to cold body by itself.

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. Both A and B are true

  2. Both A and B are false

  3. A is true but B is false

  4. A is false B is true

Show answer
Correct Option: D
Explanation:

First law of thermodynamics just states that $dQ = dW + dU $. 


It does $not$ tell us whether the process is feasible or not neither does it provide any condition to under which the body uses any energy.
Hence, A is false.

Second law of thermodynamics states that heat always flows from hot body to cold body by itself and for heat to flow from a cold body to hot body, external work should be done. 
Thus, B is true.

The coefficient of performance of a refrigeration working between ${ 10 }^{ \circ  }C$ and ${ 20 }^{ \circ  }$ C is :-

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. 1

  2. 14.15

  3. 29.3

  4. 3.53

Show answer
Correct Option: B

The work done in heating on emole of an ideal gas at constant pressure from ${ 15 }^{ 0 }C\quad to\quad { 25 }^{ 0 }C$ is

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. 1.987 cal

  2. 198.7 cal

  3. 9.935 cal

  4. 19.87 cal

Show answer
Correct Option: D

A household refrigerator with a coefficient of performance $1.2$ removes heat from the refrigerated space at the rate of $60kJ/min$. What would be cost of running this fridge for one month (30 days) (assuming each day it is used for $4$ hours and cost of one electrical unit is $6$ Rs.)

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. $180$ Rs.

  2. $300$ Rs.

  3. $480$ Rs.

  4. $600$ Rs.

Show answer
Correct Option: D

Which of the following expressions is known as Clausius inequality?

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. $\oint \frac{dq}{T}\leq 0$

  2. $\oint \frac{dq}{T}= 0$

  3. $\oint \frac{T}{dq}\leq 0$

  4. $\oint \frac{dq}{T}\geq \leq 0$

Show answer
Correct Option: A
Explanation:
$(A)\ \phi \dfrac{dq}{T} \le 0$
because according to Clausius statement, it is impossible to construct a device which operate is one a cycle and produce no other effect that transfer of heat from cold body to the hot one.

if Planck's constant h taken into a new systme of units in which new unit of mass is 10 g, new unit of length is 5 m, new unit of time is 100 s, then the value of planck's constant in new systme is $\left( {Given\;h = 6.6x{{10}^{ - 34}}\;js} \right)$

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. 6.6 $x{10^{ - 34}}\;new\;unit$

  2. 2.64 $x{10^{ - 31}}\;new\;unit$

  3. 26.4 $x{10^{ - 31}}\;new\;unit$

  4. 26.4 $x{10^{ - 33}}\;new\;unit$

Show answer
Correct Option: D

Which statement is true about 2nd law of Thermodynamics?

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. Heat can be converted to into work without changes in system or surroundings

  2. It is possible to construct a perpetual motion machine of second kind

  3. All spontaneous process are thermodynamically irreversible

  4. All spontaneous process are thermodynamically reversible

Show answer
Correct Option: C
Explanation:

 2nd law of Thermodynamics states that all spontaneous process are irreversible 

Value of planck's constant is

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. $6.6 \times 10^{-34} Js$

  2. $6.4 \times 10^{-26} Js$

  3. $6.8 \times 10^{-27} Js$

  4. $6.6 \times 10^{-28} Js$

Show answer
Correct Option: A
Explanation:

Value of Planck's constant, $h=6.6 \times 10^{-34} Js$

Hence, option A is correct.

The temperature below which a gas cannot be liquefied is called 

physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

  1. Inversion temperature

  2. Neutral temperature

  3. Critical temperature

  4. Curie temperature

Show answer
Correct Option: C