Tag: second law of thermodynamic

Questions Related to second law of thermodynamic

The statement "It is impossible  to construct a heat engine which can convert heat directly to work completely" was given by

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

  1. Clausius

  2. Carnot

  3. Plank

  4. Kelvin & Plank

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Correct Option: D
Explanation:

The second law of thermodynamics states , that it is impossible to construct a heat engine , operating in cycle , which extracts heat and can convert it all to useful work .In other words , it is impossible for a heat engine to convert heat completely in work .This statement is given by Kelvin & Plank .

The second law of thermodynamics says that in a cyclic process

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

  1. Work cannot be converted into heat

  2. Heat cannot be converted into work

  3. Work cannot be completely converted into heat

  4. Heat cannot be completely converted into work

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Correct Option: D
Explanation:

Second law of thermodynamics states that in a cyclic process heat cannot be converted completely into work because attainment of $0K$ temperature is impossible.

A new soft drink bottle is opened, allowing gas to escape into the atmosphere. As the gas escapes, its degree of disorder increases. Identify by which of the following law this can be explained ?

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

  1. First law of thermodynamics (conservation of energy)

  2. Second law of thermodynamics (law of entropy)

  3. Ideal gas law

  4. Heat of fusion and heat of vaporization equation

  5. Heat engine efficiency

Show answer
Correct Option: B
Explanation:

The second law of thermodynamics states that the total entropy of an isolated system always increases over time, or remains constant in ideal cases where the system is in a steady state or undergoing a reversible process. Thus an opened bottle allows gas to escape since the entropy increases(disorderliness increases) over time.

Which statement is true for second 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 flow spontaneously from a cold object to a hot object.

  2. You can not create a heat engine which extracts heat and converts it all to useful work.

  3. According to Plank-Kelvin's law under some circumstances a perfect heat engine is possible.

  4. None of these.

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Correct Option: B
Explanation:

The second law of thermodynamics states , that it is impossible to construct a heat engine , operating in cycle , which extracts heat and can convert it all to useful work .In other words , it is impossible for a heat engine to convert heat completely in work .

The efficiency of a heat engine is ,
            $\eta=1-\frac{Q _{2}}{Q _{1}}$
if $Q _{2}=0$ i.e. heat is not given to sink , it means total heat absorbed is converted into work , then
            $\eta=1$ , which is practically not possible .

A heat engine absorbs $Q _1$ heat from hot reservoir and work produced by engine is $W$, then:

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

  1. $Q _1$ is always $= W$

  2. only in some special cases $Q _1 = W$ otherwise $Q _1$ is greater than $W$

  3. $Q _1$ is always less than $W$

  4. $Q _1$ is always greater than $W$

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Correct Option: D
Explanation:

In a heat engine , if $Q _{1}$ is the heat absorbed from reservoir , $W$ be the work done by engine and let $Q _{2}$ be the heat given to sink , then by the first law of thermodynamics 

       $Q _{1}-Q _{2}=W$    (internal energy$dU=0$ for cyclic process)
this equation gives that $Q _{1}$ is always greater than $W$ .

When water freezes, its molecules take on a more structured order. Why doesn't this contradict the Second Law of Thermodynamics? 

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

  1. Because the density of the water is decreasing

  2. Because the water is gaining entropy as it goes from liquid to solid state

  3. Because the waters internal energy is decreasing

  4. Because the surroundings are losing entropy

  5. Because the surroundings are gaining entropy

Show answer
Correct Option: E
Explanation:

The Second Law of Thermodynamics tells us that the total amount of disorder, or entropy, in the universe is increasing. The entropy in a particular system can decrease, as with water molecules when they turn to ice, but only if the entropy in the surroundings of that system increases to an equal or greater extent. The Second Law of Thermodynamics holds, but only because the surroundings are gaining entropy, so the correct answer is E . Answer D refers to the key part of the answer, but gives the wrong information about the change in entropy of the surroundings. 
Answer C is not correct. This is an explanation for why the water does not lose heat when it freezes: it is, in fact, losing internal energy. This is an instance of the First Law of Thermodynamics, which states that the change in a systems internal energy is equal to the value of the heat transfer in the system minus the work done by the system. 

Which of the following laws of thermodynamics leads to the inference that it is difficult to convert whole of heat into work :

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

  1. zeroth

  2. second

  3. first

  4. third

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Correct Option: B
Explanation:

The second law of thermodynamics states that when energy change from one form to another form, entropy in a closed system increases.

In other words it can be stated as,
It is impossible to construct a device which produces no other effect than transfer of heat from lower temperature body to higher temperature body.
Hence it is clear that second law of thermodynamics leads to the interference that is difficult to convert whole of heat into work.

The second law of thermodynamics implies : 

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

  1. whole of heat can be converted into mechanical energy

  2. no heat engine can be 100% efficient

  3. every heat engine has an efficiency of 100%

  4. a refrigerator can reduce the temperature to absolute zero

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Correct Option: B
Explanation:

second law of thermodynamics states that ,

"It is impossible to construct a device which produces no other effect than transfer of heat from lower temperature body to higher temperature body."
$\therefore$ The second law of thermodynamics implies that no heat engine can be 100% efficient.

For the conversion of liquid into a solid :

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

  1. orderliness decreases and entropy decreases

  2. orderliness increases and entropy increases

  3. both are not related

  4. orderliness increases and entropy decreases

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Correct Option: D
Explanation:

Entropy is related to the degree of order in the structure of a system and the second law of thermodynamics means that the system always changes from a more ordered state to a less ordered state in any isolated system.


In the solid phase, the molecules are arranged in a very orderly array. Each atom has a definite equilibrium location in the regular array of atoms and it can only move around with small displacements from its equilibrium position. In the gas phase, the molecules are far apart from each other and move around almost independently from each other in random fashion. In the liquid phase the situation is intermediate, being neither as orderly as in the solid nor as random as in the gas.

Therefore, in the phase transition from liquid into a solid, the $orderliness$ of the molecules $increases$. As the Entropy is a quantity to measure the order of a system. The $entropy$ of a system $decreases$ when the system undergoes a phase transition from liquid to solid.

Hence, $orderliness$ $increases$ $and$ $entropy$ $decreases.$
Therefore, the correct option is $'D'.$

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 ($Q _{1}$) ,

          $\eta=\frac{W}{Q _{1}}$