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Explain why a Carnot engine cannot have ...

Explain why a Carnot engine cannot have 100% efficiency?

A

prevent radiation

B

find ideal sources

C

reach absolute zero temperature

D

eliminate friction

Text Solution

Verified by Experts

The correct Answer is:
C
The efficiency of Carnot engine is `eta=1-(T_2"/"1T_1)`
Where,`T_1` is the temperature of the source and `T_2` that of sink.
Since, ` (T_2)/(T_1)=(Q_2)/(Q_1)`
So, `et=1 -(Q_2)/(Q_1)`
To obtain 100% efficiency (i.e.,`eta=1),Q_2` must be zero i.e., if a sink at absolute zero would be available, all the heat taken from the source would have been converted into work.
The temperature of sink means a negative temperature on the absolute scale at which the efficiency of engine is greater than unity. This would be a violation of the 2nd law of thermodynamics. Hence, a negative temperature on the absolute scale is impossible. Hence, we cannot reach absolute zero temperature.
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Knowledge Check

  • Carnot engine is

    A
    1. reversible engine
    B
    2. operating between two temperatures `T_(1)` (source) and `T_(2)` (sink) have maximum efficiency
    C
    3. consisting of two isothermal processes connected by two adiabatic processes
    D
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  • A frictionless heat engine can be 100% efficient only if its exhaust temperature is

    A
    `0^(@)C `
    B
    `0K`
    C
    equal to its input temerpature
    D
    half of its input temperature

  • Assetion : No engine can have efficiencyt greater than that of the carnot engine Reason : The efficiencyt of a cornot engine is given by eta =1-(T_(2))/(T_(1))

    A
    If both assetion and reason are true and reaasons is the correct expanation of assetion
    B
    If both assetion and reason are tur but reason is not the correct explanation of assetion
    C
    If assertion is true but reason is false
    D
    If both assertion and reason are false.

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