The concepts of Energy and Power Efficiency are essential for understanding how systems use resources and how to optimize them for better performance and sustainability.
Efficiency is a way of describing how good a machine is at transferring energy into useful forms.
What is Energy Efficiency?
Energy Efficiency measures how effectively a system, device, or process converts input energy into useful output energy to perform a desired task.
It measures how efficiently Energy is converted into useful work while minimizing waste.
Formula:
where,
Example:LED Bulb and Incandescent Bulb:
An LED bulb converts about 80-90% of the electrical energy into light, with very little wasted as heat.
An Incandescent bulb, on the other hand, converts only about 10% of the electrical energy into light — the rest is lost as heat.
The LED bulb is more energy-efficient.
What is Power Efficiency?
Power efficiency is the ratio of useful output power to the total input power supplied to a system or device.
It measures how efficiently Power is converted into useful work while minimizing waste.
Formula:
Where,
Output power is the power used to perform the desired task.
Input power is the total power supplied to the system.
The rest is usually lost as heat, noise, or vibration.
Example:
Fan A is more power-efficient because it converts more of the input power into useful mechanical power, while wasting less power as heat, noise, or friction.
How to Calculate Efficiency?
Efficiency tells us how well a device or system converts input energy or power into useful output.
It’s usually expressed as a percentage.
Formula for Energy Efficiency:
Formula for Power Efficiency:
Steps to Calculate Efficiency:
1
Find the input value (energy or power supplied to the system).
2
Find the useful output value (energy or power used for the intended purpose).
3
Apply the formula.
4
Multiply by 100 to convert it into a percentage.
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A light bulb takes 100 joules of electrical energy and produces 60 joules of light energy. The rest is lost as heat. Calculate the energy efficiency of the light bulb.
SOLUTION
1
Step #1: Find the input value
Total Input Energy = 100 J
2
Step #2: Find the useful output value:
Useful Output Energy = 60 J
3
Step #3: Apply the formula:
4
Step #4: Multiply by 100:
The light bulb has an energy efficiency of 60%.
Final Answer:60%
Solved Example
A water pump uses 500 watts of electrical power and delivers 400 watts of useful mechanical power to pump water. Calculate the power efficiency of the pump.
SOLUTION
1
Step #1: Find the input value
Total Input Power = 500W
2
Step #2: Find the useful output value:
Useful Output Power = 400W
3
Step #3: Apply the formula:
4
Step #4: Multiply by 100:
The water pump has a power efficiency of 80%.
Final Answer:80%
Frequently Asked Questions
Solution:
Efficiency measures how well something (a machine, device, or system) converts input (like energy) into useful output without wasting resources.
Solution:
We can reduce unwanted energy transfers by using lubrication to reduce friction, insulation to prevent heat loss, and streamlining to reduce air resistance.
Solution:
Energy efficiency means using less energy to do the same job. It helps save money and reduces waste.
Example:
An LED bulb (energy-efficient) gives the same light as an old incandescent bulb but uses much less electricity.
Solution:
Power efficiency measures how well a device converts input power (electricity) into useful output (like light, motion, or computation) without wasting it as heat.
Example:
A 90% efficient power supply wastes only 10% of electricity as heat, while a 60% efficient one wastes 40%.
Solution:
Saves money (lower electricity bills).
Reduces pollution (less energy waste = fewer power plants needed)
