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The MCQs below are drawn from the Current Affairs subject category.
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65021
Who suggested that energy is radiated or absorbed in discrete packets called quanta?
A. Lummer
B. Max. Planck
C. Boltzmann
D. Stefan
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Explanation
Max Planck proposed that energy is emitted or absorbed in discrete quanta, initiating quantum theory.
65022
Tick which of the following is not a state variable?
A. Entropy
B. Volume
C. Heat energy
D. Pressure
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Explanation
The block's explanatory answer states A; heat is energy in transit, not a state function, so it is not a state variable.
65023
In an isothermal process, the internal energy of the system:
A. Increases
B. Decreases
C. Remains constant
D. None of these
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Explanation
The block's explanatory answer gives C; in an isothermal process the temperature is constant, so the internal energy (for an ideal gas) remains constant.
65024
No entropy change is associated with
A. isochoric process
B. isothermal process
C. adiabatic process
D. isobaric process
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Explanation
A reversible adiabatic (isentropic) process has no change in entropy, so adiabatic is the correct choice.
65025
A Carnot engine, whose efficiency is 40%, receives heat at 500 K. If its efficiency is 50%, then the intake temperature for the same exhaust temperature is
A. 600 K
B. 800 K
C. 700 K
D. 900 K
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Explanation
For e1=0.4 with Th1=500K, Tc = Th1(1−e1)=500×0.6=300K; for e2=0.5, Th2 = Tc/(1−e2)=300/0.5=600K.
65026
The highest efficiency of a heat engine whose low temperature is 17 ℃ and the high temperature of 200 ℃ is
A. 20%
B. 30%
C. 40%
D. 35%
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Explanation
Carnot efficiency = 1 - Tc/Th with temperatures in K: 1 - (290/473) ≈ 0.387 ≈ 38.7%, closest to 40%.
65027
Who developed hypothetical heat engine that has the maximum possible efficiency in 1824?
A. Rudolf Diesel
B. August Otto
C. Saadi Carnot
D. Karl Benz
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Explanation
Sadi Carnot (here OCRed as 'Saadi Carnot') described the ideal heat engine in 1824, giving the maximum efficiency concept.
65028
Who described an ideal heat engine in 1840?
A. Saadi Carnot
B. Bragg
C. Boyle
D. Kelvin
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Explanation
Sadi Carnot is historically associated with the concept of an ideal heat engine, so Carnot is the selected answer.
65029
Who originated the idea of heat death of the universe in 1852?
A. James Thomson
B. John Thomson
C. Lord Kelvin
D. Saadi Carnot
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Explanation
Lord Kelvin (William Thomson) is credited with originating the idea of the heat death of the universe around the mid-19th century.
65030
When the temperatures of source and sink of a heat engine become equal, the change in entropy will be:
A. Zero
B. Minimum
C. Maximum
D. None of these
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Explanation
The provided explanatory text states that when T1 = T2 the change in entropy is maximum (as given in the OCR block).
