Tag: the second law of thermodynamics

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Questions Related to the second law of thermodynamics

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

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.

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  1. 1.987 cal

  2. 198.7 cal

  3. 9.935 cal

  4. 19.87 cal
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work done at constant pressure W = n * R * deltaT. n = 1 mole, R = 1.987 cal/mol*K, deltaT = 25 - 15 = 10 K. W = 1 * 1.987 * 10 = 19.87 cal.

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

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.)

  1. $180$ Rs.

  2. $300$ Rs.

  3. $480$ Rs.

  4. $600$ Rs.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Heat removed = 60 kJ/min. Work input = Heat / COP = 60 / 1.2 = 50 kJ/min. Total time = 30 days * 4 hours/day * 60 min/hour = 7200 min. Total work = 50 kJ/min * 7200 min = 360,000 kJ. 1 unit = 1 kWh = 3600 kJ. Units = 360,000 / 3600 = 100 units. Cost = 100 units * 6 Rs/unit = 600 Rs.

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

Which of the following expressions is known as Clausius inequality?

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

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

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

  4. $\oint \frac{dq}{T}\geq \leq 0$
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

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 $\left( {Given\;h = 6.6x{{10}^{ - 34}}\;js} \right)$

  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 $x{10^{ - 33}}\;new\;unit$
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice physics heat engine: second law of thermodynamics second law of thermodynamics the second law of thermodynamics second law of thermodynamic

Which statement is true about 2nd law of Thermodynamics?

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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