Tag: second law of thermodynamic

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Questions Related to second law of thermodynamic

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

Consider a new system of units in which c (speed of light in vacuum), h(Planck's constant) and G (gravitational constant) are taken as fundamental units. Which of the following would correctly represent mass in this new system?

  1. $\sqrt{\dfrac{hc}{G}}$

  2. $\sqrt{\dfrac{Gc}{h}}$

  3. $\sqrt{\dfrac{hG}{c}}$

  4. $\sqrt{hGc}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Consideration anew system of units in which speed of light in vaccum$=e$Plank's constant$=h$

Gravitational constant$=G$
Mass in the new system
$F=\cfrac{1}{2}mv^2=h\gamma$
Now,
Using the method of dimension we say that,
Here
${e}=LT^{-1}$
$[G]=M^{-1}L^3T^{-2}$
$[h]=M^1L^2T^{-2}$
Let, $mac^xG^0h^z$
By substituting the dimension of each quantity in both the sides
$M=(LT^{-1})^x(M^{-1}L^3T^{-2})^y(ML^2T^{-1})^z\M=(M^{y+z}L^{x+3y+2z}T^{x-2y-x})$
By equating the power of $M,L\quad and T$ in both the sides
$-y+z=1\x+3y+2z=0\-x-2y-z=0$
By solving the above equations
We get,
$x=\cfrac{1}{z},y=-\cfrac{1}{z},z=\cfrac{1}{z}$
So, $[m]=e^{1/2}G^{-1/2}h^{1/2}\ \quad=\sqrt{\cfrac{hc}{G}}$

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

For a gas $\cfrac{R}{C _{p}}=0.4$. For this gas calculate the following-

  1. atomicity and degree of fredom

  2. value of $C _{v}$ and $\gamma$

  3. mean gram-molecular kinetic energy at $300\ k$ temperature

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given R/Cp = 0.4, we find Cp = R/0.4 = 2.5R. Since Cp - Cv = R, we get Cv = 1.5R. The ratio of specific heats γ = Cp/Cv = 2.5R/1.5R = 5/3 = 1.67. This corresponds to a monatomic gas with f = 3 degrees of freedom. Option B correctly asks for Cv and γ values, which are the natural quantities to calculate from the given.

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

Efficiency of engine is $n _{1}$ at $T _{1}$= $200^\circ C$ and $T _{2}$ = $0^\circ C$ and $n _{2}$ at $T _{1} = 0^\circ C$ and $T _{2}=-200^\circ C$. Find the ratio of $\cfrac {n _{1}}{n _{2}}$

  1. $1.00$

  2. $0.721$

  3. $0.577$

  4. $0.34$4
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Efficiency n = 1 - (T2/T1). For n1: T1 = 473K, T2 = 273K, n1 = 1 - (273/473) = 200/473. For n2: T1 = 273K, T2 = 73K, n2 = 1 - (73/273) = 200/273. Ratio n1/n2 = (200/473) * (273/200) = 273/473 approx 0.577.

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

An ideal heat engine has an efficiency $ \eta$ . The co-efficient of performance of the engine when driven backward is 

  1. $1-\dfrac{1}{\eta}$

  2. $\dfrac{\eta}{1- \eta}$

  3. $\dfrac{1}{\eta}-1$

  4. $\dfrac{1}{1- \eta}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Efficiency n = W/Q1 = (Q1-Q2)/Q1. Coefficient of performance (COP) for a refrigerator is Q2/W. Since W = Q1 - Q2, COP = Q2/(Q1-Q2). Dividing by Q1 gives (Q2/Q1) / (1 - Q2/Q1). Since n = 1 - Q2/Q1, Q2/Q1 = 1 - n. Substituting gives (1-n)/n = (1/n) - 1.

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

Heat flows between two bodies due to difference in their temperature.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat is defined as the energy which passes between two objects because of the difference in temperature. Thus energy may pass between them, but not heat. It is possible that the energy absorbed may increase the temperature, particularly if work is done, but this is not heat transfer.


Heat flows between two bodies due to difference in their temperature.

Option A is true

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

That 'Entropy of a system increases in all spontaneous processes' is  known as

  1. 1 st law of Thermodynamics

  2. 2nd law of Thermodynamics

  3. Zeroth law of Thermodynamics

  4. 3rd law of Thermodynamics
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems spontaneously evolve toward thermodynamic equilibriumthe state of maximum entropy

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

A bullet of mass 100g moving with 20 m/s strikes a wooden plank and penetrates upto 20cm . Calculate the resistance offered by wooden plank

  1. $10^2 N$

  2. $10^3N$

  3. $10^4N$

  4. $10^5 N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using the work-energy theorem, initial kinetic energy = (1/2)mv^2 = 0.5 x 0.1 kg x (20 m/s)^2 = 20 J. This work is done against the resistance force over 0.2 m distance: F x d = 20 J, so F = 20/0.2 = 100 N = 10^2 N. The wooden plank offers constant resistance decelerating the bullet to rest.

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 option are related with the second law of thermodynamics (law of entropy)?

  1. The heat lost by one object must be gained by another object

  2. Heat flow naturally from a hotter body to a cooler body

  3. Celsius degrees and Kelvin degrees are equivalent

  4. Heat can be transformed into work

  5. The average kinetic energy of molecules is proportional to temperature
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The second law of thermodynamics says that heat flows 'naturally' from an object at a higher temperature to an object at a lower temperature, and heat doesn’t flow in the opposite direction of its own accord, since the entropy in such a process increases. 

The reverse is not possible due to decrease in entropy in such a process.

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 statement is true as per the second law of thermodynamics for an isolated, ordered system?

  1. Heat will flow into the system

  2. Heat will flow out of the system

  3. Work will be done by the system

  4. Work will be done on the system

  5. The entropy withing the system will increase
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The second law of thermodynamic states that the entropy of an isolated system increases over time and remain constant for reversible process.