# Which law of thermodynamics best describes why a car’s engine Cannot be 100% efficient?

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We know from the second law of thermodynamics that a heat engine cannot be 100 percent efficient, since there must always be some heat transfer Qc to the environment. … He devised a theoretical cycle, now called the Carnot cycle, which is the most efficient cyclical process possible.

## Why is it that no engine can be 100% efficient What law states this?

The fact that efficiencies can’t be 100% attainable is primarily due to their working temperatures, at which they enter as heat and at which they are rejected to the sink. According to Second law of thermodynamics, even an ideal, frictionless engine would be unable to convert all its heat into work.

## Why can’t we get 100% efficiency in a thermodynamic cycle?

This is because it is not possible to convert the entire heat input to work output, a portion of the heat has to be rejected to a sink (Second Law of Thermodynamics). In actual engines the efficiency is even less due to friction losses, burning characteristics etc.

## Why is a system not 100% efficient?

It is not possible to have an efficiency of greater than 1 or an efficiency percentage greater than 100%. This would mean that more energy is being transferred than is being supplied, which would mean that energy is being created. This would break the law of conservation of energy.

## Is the Carnot cycle 100% efficient?

The efficiency of Carnot engine = 1 – (sink temperature / source temperature). As per the Kelvin Planck statement no engine has 100 % efficiency. Sink temperature will always be less than that of source temperature. Thus efficiency of Carnot cycle becomes less than 100 %.

## Can a system be 100% efficient?

Because of conservation of energy EVERY system produces an equal amount of energy that’s put into the system. … So if you put in 100 watts of power and get 50 watts of light the system is 100% efficient. There is a principle called “unity efficiency” that can allow you to produce MORE than 100% of the input.

## Why real processes are irreversible?

An irreversible process is a process that cannot return both the system and the surroundings to their original conditions. … Four of the most common causes of irreversibility are friction, unrestrained expansion of a fluid, heat transfer through a finite temperature difference, and mixing of two different substances.

## Why are heat engines inefficient in general?

Why are heat engines inefficient, in general? a. Temperatures are so high that a great deal of heat is lost to the environment. … Heat engines attempt to convert the worst source of energy into the best.

## Why is Carnot efficiency less than 1?

Because according to Second law of thermodynamics ( KELVIN- PLANK STATEMENT ) some part of input energy always goes into the sink i.e low temperature reservoir and gets wasted. Hence , efficiency is less than 1 ..

## Can a perfectly efficient system ever be created?

The fact is, you can’t make a super-efficient system without any waste. No matter how good of an engineer you are, you can’t invent a perfect engine. … Simply put, a heat engine is a machine or system that converts heat into other forms of energy.

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## Is a heater 100% efficient?

Electric heaters are all considered to be 100% efficient, because they turn all the electricity they use into heat, but this does not mean they are cheap to run.

## Why is Carnot cycle Impossible?

The most efficient heat engine cycle is the Carnot cycle, consisting of two isothermal processes and two adiabatic processes. … It is not a practical engine cycle because the heat transfer into the engine in the isothermal process is too slow to be of practical value.

## Is a Carnot cycle reversible?

The Carnot heat-engine cycle described is a totally reversible cycle.

## What is Carnot principle?

Carnot’s theorem, developed in 1824 by Nicolas Léonard Sadi Carnot, also called Carnot’s rule, is a principle that specifies limits on the maximum efficiency any heat engine can obtain. The efficiency of a Carnot engine depends solely on the temperatures of the hot and cold reservoirs. 