# Frequent question: Is it possible to construct a reversible heat engine of unity efficiency?

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## Can the efficiency of heat engine be greater than unity?

The fraction of the heat input that is converted to net work output is a measure of the performance of a heat engine and is called the thermal efficiency. The thermal efficiency of a heat engine is always less than unity since both QL and QH are defined as positive quantities.

## Why is it impossible to create a 100% efficient machine?

Explanation: No machine is free from the effects of gravity, and even with wonderful lubrication, friction always exists. The energy a machine produces is always less than the energy put into it (energy input). … That is why 100% efficiency in machines shall not be possible.

## Can we consider heat engine 100% efficient Why?

It is impossible for heat engines to achieve 100% thermal efficiency () according to the Second law of thermodynamics. This is impossible because some waste heat is always produced produced in a heat engine, shown in Figure 1 by the term.

## What is the efficiency of a reversible heat engine?

The amount of heat that is converted to work in a reversible heat engine is always more than the amount of heat converted to work in an irreversible heat engine because unlike irreversible heat engines, there is no loss of energy in a reversible heat engine.

## Do all reversible heat engines have the same efficiency?

All reversible heat engines operating between the two given thermal reservoirs have the same efficiency. The efficiency of reversible heat engine does not depend on the working fluid, it depends only on the temperature of the reservoirs between which it operates.

## Is it possible to construct a heat engine that produces no thermal pollution?

Is it possible to construct a heat engine, which is free from thermal pollution? No, as in accordance with second law of thermodynamics, whole of heat cannot be converted into work.

## What determines the maximum possible efficiency of a heat engine?

The maximum theoretical efficiency of a heat engine (which no engine ever attains) is equal to the temperature difference between the hot and cold ends divided by the temperature at the hot end, each expressed in absolute temperature.

## Why no heat engine can be constructed having efficiency equal to or greater than unity?

Since heat energy can never be transformed completely into mechanical energy, so the efficiency of a heat engine can never be 100 per cent. … Even if the design of heat engines is improved further, it will never be possible to convert all the heat supplied to an engine into mechanical energy or work.

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## Is it possible to have more than 100% efficiency?

Even though the energy efficiency calculated using common methods exceeds 100%, more than 100% of the theoretical energy content of the fuel, expressed as the Higher Heating Value (HHV), is naturally not recovered.

## Why are heat engines not 100% efficient?

A heat engine is considered to be 100% efficient if only all the heat is converted into useful work or mechanical energy. Since heat engines cannot convert all the heat energy into mechanical energy, their efficiency can never be 100%.