Question

the efficiency of an actual machine is never 100 percent
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Answer 1

Efficiency of a real machine is never 100% because some of the input energy is lost in overcoming frictions between the movable parts of the machine. Hence it's output energy is always less than the input energy

as we know

output work /input work *100 =efficiency% hence efficiency in real machine is less than 100%

Answer 2

               yes, the efficiency of an engine is never 100 %.

reason:- let the heat Q₁ drawn from the source and some work is to done,and then remaining heat transferred to sink at lower temperature.

efficiency of heat engine:-   1 - Q₂/Q₁

HERE ,100%efficiency means Q₂ becomes 0, but is not possible.if some amount of heat is taken out from source and some work is to be done, then it is necessary that some heat is must transfered to sink. i.e Q₂≠0

SO IN ORDER TO SATISFY SECOND LAW OF THERMODYNAMICS, the efficiency of any self acting machine and engine is never 100%