Question

Even Carnot engine does not give $100\%$ efficiency because we cannot
A. Prevent radiation
B. Find ideal source
C. Reach absolute zero temperature
D. Eliminate friction

Answer 1

Carnot engine is an ideal thermodynamic cycle. It tells the maximum efficiency possible to achieve. According to the ${2^{nd}}$ law of thermodynamics” It is impossible to convert all the heat extracted from a hot source into work”. In other words, practically, it is not possible to have an engine with $100\%$ efficiency.

Complete answer:
Carnot’s heat engine is an ideal heat engine that is free from all imperfections of an actual engine. We can compare the efficiency of a real engine with Carnot’s ideal engine and try to improve it, but it can never be perfect and can’t give $100\%$ efficiency because no matter how we try, some energy gets lost in overcoming friction, electrical resistance, and other disruption.
In other words, we can’t have an ideal source and ideal sink which completely transfers energy from one body to another without some loss of energy or some energy consumption.
$100\%$ efficiency is not possible because some of the heat of the source will get used up for overcoming friction and other force and therefore full heat of source will not be transferred to the sink and therefore there exists no ideal source.
Therefore, the correct option is option (B). Even the Carnot engine does not give $100\%$ efficiency because we cannot can’t find the ideal source.

Note:
Carnot ‘s heat engine, which is an ideal heat engine is not practically possible because it requires a source and sink of infinite heat capacities and the working engine transfers all energy from source to sink without consuming any energy. In it, dissipative forces are absent.