In the study of 'Work, Energy, and Power', scientists and engineers design machines (like car engines, electric motors, or even simple pulleys) to make work easier. However, no machine is perfect. To measure how good a machine is at its job, we calculate its 'Efficiency'.
An 'Ideal Machine' is a theoretical, imaginary machine that has no friction and is 100% efficient. It does not exist in reality.
LED bulbs are highly efficient because they convert almost all electrical input into Light output, whereas old incandescent bulbs wasted 90% of their energy generating useless Heat.
Efficiency (usually denoted by the Greek lowercase letter eta, $\eta$) is defined as the ratio of the useful energy output produced by a machine to the total energy input given to the machine.
The standard mathematical formula is: Efficiency ($\eta$) = $\frac{\text{Useful Work Output}}{\text{Total Work Input}}$
In real-life engineering, efficiency is almost always expressed as a percentage (%). To get this, simply multiply the result by 100.
Efficiency (%) = $\left( \frac{\text{Power Output}}{\text{Power Input}} \right) \times 100$
If you put 100 Joules of energy (petrol) into a car, you will never get 100 Joules of forward movement out of it.
No. According to the Law of Conservation of Energy, you cannot create energy out of nothing. A machine cannot give out more energy than you put into it.
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