M.C.Q (1 Marks)

MCQ 511 Mark

An engine has an efficiency of $\frac16$ when the temperature of sink is reduced by 62°C, its efficiency is doubled, temperature of the source is:

A
37°C.
B
62°C.
C
99°C.
D
124°C.

Answer

99°C.

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MCQ 521 Mark

A mixture of gases undergoing explosive chemical reaction:

A
Is not in equilibrium state during explosion.
B
May have variable temperature and pressure values during explosion.
C
Finally the gas will attained equilibrium state with its surroundings.
D
All of the above.

Answer

All of the above.

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MCQ 531 Mark

The internal energy of an ideal gas depends on:

A
Pressure.
B
Volume.
C
Temperature.
D
Size of molecules.

Answer

Temperature.

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MCQ 541 Mark

If m is the mass, $\theta$ is temperature and 'a' is specific heat, then thermal capacity K is given by:

A
$\text{K}=\text{ms}\theta$
B
$\text{K}=\text{m}\theta$
C
$\text{K}=\frac{\text{ms}}{\theta}$
D
$\text{K}=\text{ms}$

Answer

$\text{K}=\text{ms}$

Explanation:

Thermal capacity = Mass × Specific heat = m × s

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MCQ 551 Mark

According to second law of thermodynamics:

A
A heat engine cannot have efficiency equal to 1.
B
A refrigerator (or heat pump) could have infinite value of coefficient of performance.
C
A heat engine can convert heat fully in to work.
D
Heat can flow from cold to hot body.

Answer

A heat engine cannot have efficiency equal to 1.

Explanation:

Second law puts limitation on the efficiency of a heat engine and on the coefficient of performance of a refrigerator. Heat engine cannot have efficiency equal to 1 and a refrigerator cannot have infinite value of coefficient of performance.

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MCQ 561 Mark

An ideal gas having molar specific heat capacity at constant volume is $\frac32\text{R}$ the molar specific heat capacities at constant pressure is:

A
$\frac12\text{R}$
B
$\frac52\text{R}$
C
$\frac72\text{R}$
D
$\frac92\text{R}$

Answer

$\frac52\text{R}$

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MCQ 571 Mark

One mole of an ideal gas at an initial temperature of T, K does 6R joule of work adiabatically. If the ratio of specific heats of this gas at constant pressure and at constant volume is $\frac53,$ the final temperature of the gas will be:

A
(T + 4)K
B
(T - 4)K
C
(T + 2.4)K
D
(T - 2.4)

Answer

(T - 4)K

Explanation:

Here, T₁ = T, W = 6R

$\gamma=\frac{\text{C}_\text{P}}{\text{C}_\text{V}}=\frac53,\text{T}_2=?$

In and adiabatic process,

$\text{W}=\frac{\text{R}(\text{T}_2-\text{T}_1}{1-\gamma}$

$\text{6R}=\frac{\text{R}(\text{T}_2-\text{T}_1)}{1-\frac53}$

$\text{T}_2-\text{T}=6\Big(-\frac23\Big)=-4$

$\text{T}_2-\text{(T}-4)\text{K}$

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MCQ 581 Mark

For a heat engine the heat taken from the hot source is Q₁. So,

A
Q₁ = Q₂ - Q
B
Q₂ = W
C
Q₁ = Q₂
D
None of these.

Answer

None of these.

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MCQ 591 Mark

Coefficient of performance for heat pump is (when heat supplied by system is Q₁):

A
$\alpha=\frac{\text{Q}_2}{\text{W}}$
B
$\alpha=\frac{\text{Q}_1}{\text{W}}$
C
$\alpha=\frac{\text{Q}_1}{\text{Q}_2}$
D
$\alpha=\frac{\text{Q}_2}{\text{Q}_1}$

Answer

$\alpha=\frac{\text{Q}_2}{\text{W}}$

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MCQ 601 Mark

If the coefficient of performance of a refrigerator is 5 and operates at the room temperature (27°C), find the temperature inside the refrigerator.

A
-23°C.
B
23°C.
C
40°C.
D
-40°C.

Answer

-23°C.

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MCQ 611 Mark

According to Carnot, which type of engine working between two temperatures T and T₂ have maximum efficiency?

A
Reversible engine.
B
Irreversible engine.
C
External combustion engine.
D
Diesel engine.

Answer

Reversible engine.

Explanation:

For reversible engine, according to Carnot, efficiency is maximum.

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MCQ 621 Mark

During melting of a slab of ice at 273°K at atmospheric pressure:

A
Positive work is done by ice water system on the atmosphere.
B
Positive work is done on ice water system by the atmosphere.
C
Internal energy of ice water system increases.
D
Internal energy of ice water system decreases.

Answer

Positive work is done on ice water system by the atmosphere.

Explanation:

During melting of ice, volume decreases. Therefore, positive work is done on the system by the atmosphere. Also heat spent in melting increases the internal energy of ice-water system.

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MCQ 631 Mark

Which condition is true for an ideal Carnot engine which have 100% efficiency?

A
Temperature of sink source T₁ = 0K.
B
Temperature of sink T₂ = 0K.
C
Temperature of sink source T₁ = 1.0K.
D
None of the above.

Answer

Temperature of sink T₂ = 0K

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MCQ 641 Mark

The door of a running refrigerator inside a room is left open. The correct statement out of the following ones is:

A
The room will be cooled slightly.
B
The room will be warmed up gradually.
C
The room will be cooled to the temperature inside the refrigerator.
D
The temperature of the room will remain unaffected.

Answer

The room will be warmed up gradually.

Explanation:

Coefficient of performance of refrigerator is,

$\frac{\text{Q}_2}{\text{W}}=\frac{\text{T}_2}{\text{T}_1-\text{T}_2}$

When the door of a running refrigerator inside a room is left open, T₂ → T₁. Coefficient of performance increases. Q₂ increases.

Therefore, heat energy given to the room increases. Hence the room will be warmed up gradually.

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MCQ 651 Mark

If a system is in thermodynamic equilibrium with its surroundings, it means:

A
Temperature of system and surroundings must be same.
B
Pressure, volume and temperature of system and surroundings must be same.
C
Pressure, volume and temperature of system and surroundings may be different.
D
None of the above.

Answer

Temperature of system and surroundings must be same.

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MCQ 661 Mark

If two systems are in thermal equilibrium with each other, it means their:

A
Masses are equal, temperatures may be unequal.
B
Temperatures are equal.
C
Masses and temperatures are equal.
D
None of the above.

Answer

Temperatures are equal.

Explanation:

If two systems are in thermal equilibrium with each other, it means their temperatures must be same. Masses may be equal or unequal.

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MCQ 671 Mark

If an average person jogs, he produces 14.5 × 103 cal/ min. This is removed by the evaporation of sweat. The amount of sweat evaporated per minute (assuming 1kg requires 580 × 103cal for evaparation) is

A
0.25kg
B
2.25kg
C
0.05kg
D
0.20kg

Answer

0.25kg

Explanation:

580 × 10³Calories are needed to convert 1kg H₂O into steam.

1cal will producer sweat $=\frac{1}{580\times10^{3}}$

14.5 × 10³cal will producer sweat $=\frac{14.5\times10^3}{580\times10^3}$

$=\frac{145}{5800}\text{kg }\text{per}\text{minute}=0.25\text{kg }\text{per}\text{minute}$

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MCQ 681 Mark

Which of the processes described below are irreversible?

A
The increase in temprature of an iron rod by hammering it.
B
A gas in a small cantainer at a temprature T₁ is brought in contact with a big reservoir at a higher temprature T₂ which increases the temprature of the gas.
C
A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston.
D
An ideal gas is enclosed in a piston cylinder arrangement with adiabatic walls. A weight W is added to the piston, resulting in compression of gas.

Answer

The increase in temprature of an iron rod by hammering it.
A gas in a small cantainer at a temprature T₁ is brought in contact with a big reservoir at a higher temprature T₂ which increases the temprature of the gas.
A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston

Explanation:

Key concept: Reversible process: A reversible process is one which can be reversed in such a way that all changes occurring in the direct process are exactly repeated in the opposite order and inverse sense and no change is left in any of the bodies taking part in the process or in the surroundings.
The conditions for reversibility are:

There must be complete absence of dissipative forces such as friction, viscosity, electric resistance etc. ~
The direct and reverse processes must take place infinitely slowly.
The temperature of the system must not differ appreciably from its surroundings.

Irreversible process: Any process which is not reversible exactly is an irreversible process. All natural processes such as conduction, radiation, radioactive decay etc. are irreversible. All practical processes such as free expansion, Joule-Thomson expansion, electrical heating of a wire are also irreversible.

In this case internal energy of the rod is increased from external work done by hammer which in turn increases its temperature. So, the process cannot be retraced itself.
In this process energy in the form of heat is transferred to the gas in the small container by big reservoir at temperature T
In a quasi-static isothermal expansion, the gas is ideal, this process is reversible because the cylinder is fitted with frictionless piston.
As the weight is added to the cylinder arrangement in the form of external pressure hence, it cannot be reversed back itself.

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MCQ 691 Mark

An ideal heat engine exhausting heat at 27°C is to have 25% efficiency. It must take heat at:

A
127°C.
B
227°C.
C
327°C.
D
673°C.

Answer

127°C.

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Physics M.C.Q (1 Marks)