Efficiency is defined as the ratio of work done by a machine to the work done on a machine. Every machine that we use in our lives has an efficiency that allows us to assess the performance of the machine. Percentage efficiency of some machines is given in the table.

Machine	Efficiency (%)
Heat engine	40
Solar panels	15
Steam turbine	35
Electric generator	90
Carnot engine	50

Now, answer the following questions.

(a) Which machine has the highest efficiency? What does it mean?

(b) Which machine has the lowest efficiency? What does it mean?

(c) Are these simple machines or complex machines?

(d) What is the formula to calculate efficiency of a machine?

(f) Are any of these machines ideal? If no, why?

(g) Using the Internet, find out where these machines are used.

(a) The electric generator has the highest efficiency of 90%. This means that 90% of the work done on the generator (input energy) is converted into useful electrical energy (output work), with only 10% lost as heat or other forms of energy.

(b) The solar panels have the lowest efficiency of 15%. This means only 15% of the solar energy falling on the panels is converted into electricity, while the remaining 85% is lost, mostly as heat or reflection.

(c) All of these are complex machines, since they are made of multiple components and systems working together, unlike simple machines (like lever, pulley, or wedge).

(d) Efficiency

$\text {Efficiency} (\%) = \dfrac{\text {Work done by a machine}}{\text {Work done on a machine}}\times 100\ \% = \dfrac{\text {Output energy}}{\text {Input energy}}\times 100\ \%$

(e) No, none of these machines are ideal. An ideal machine would have 100% efficiency with no energy loss. In reality, some energy is always lost as heat, sound, or friction, so no real machine can be perfectly efficient.

(f) These machines are used in the following devices :

• Heat engine → Cars, trucks, and airplanes (internal combustion engines).
• Solar panels → Rooftops, solar farms, calculators, satellites.
• Steam turbine → Power plants (coal, nuclear, geothermal).
• Electric generator → Power stations, wind turbines, hydroelectric dams.
• Carnot engine → Theoretical model studied in thermodynamics.