1. What Is Efficiency?
Efficiency tells us how well a machine or device converts input energy into useful output energy. No real machine is 100% efficient because some energy is always lost as heat, sound or friction.
1.1. Why Efficiency Matters
A highly efficient device wastes less energy and performs better. For example, LED bulbs are more efficient than old filament bulbs because they convert more electrical energy into light and less into heat.
2. Efficiency Formula
Efficiency is defined as the ratio of useful output energy (or power) to the input energy (or power).
2.1. Formula Using Energy
\( \text{Efficiency} = \dfrac{\text{Useful Output Energy}}{\text{Input Energy}} \times 100\% \)
2.2. Formula Using Power
\( \text{Efficiency} = \dfrac{\text{Useful Output Power}}{\text{Input Power}} \times 100\% \)
2.3. Understanding the Formula
If a machine receives 100 J of energy but produces only 60 J of useful work, its efficiency is:
\( \dfrac{60}{100} \times 100\% = 60\% \)
The remaining 40 J is lost as heat, sound, or friction.
3. Examples That Show Efficiency
Different devices have different efficiencies depending on how they convert energy.
3.1. Example 1: Light Bulbs
An LED bulb converts a large portion of electrical energy into light → high efficiency.
A filament bulb loses most energy as heat → low efficiency.
3.2. Example 2: Car Engine
A car engine converts chemical energy from fuel into kinetic energy. But a lot of energy is lost as heat and sound, so the overall efficiency is low (about 20–30%).
3.3. Example 3: Machines in Workshops
Machines like pumps, motors and compressors use electrical energy. The more efficient the machine, the less electricity it wastes.
4. Power and Efficiency Together
Power tells us how fast energy is being used. Efficiency tells us how much of that energy is useful.
Even a powerful machine can be inefficient if it wastes energy.
4.1. Useful Power Output
Useful power output is the portion of input power that actually does work.
\( P_{\text{useful}} = \text{Efficiency} \times P_{\text{input}} \)
4.2. Example Calculation
If a motor takes 500 W of electrical power and has an efficiency of 80%:
\( P_{\text{useful}} = 0.8 \times 500 = 400 \text{ W} \)
This means 400 W is used effectively and 100 W is wasted.
5. Why 100% Efficiency Is Impossible
In real-world machines, some energy always becomes:
- Heat due to friction
- Sound
- Vibrations
- Energy lost to surroundings
Because of these losses, no machine can be perfectly efficient.
5.1. Reducing Energy Losses
Using lubrication, minimizing friction, good machine design, and proper maintenance help improve efficiency.