Input/Output Power Calculator
Calculate efficiency from power input and output.
Formula first
Overview
This equation quantifies energy conversion efficiency by comparing the useful power output to the total power input supplied to a system. It accounts for inevitable energy losses due to friction, heat, and sound, providing a percentage that represents mechanical or electrical effectiveness.
Symbols
Variables
\eta = Efficiency, P_{out} = Power Output, P_{in} = Power Input
Apply it well
When To Use
When to use: Use this formula when analyzing the performance of engines, motors, transformers, or any system where energy is transformed. It requires that both input and output power values are expressed in the same units, such as Watts or Horsepower.
Why it matters: Efficiency is fundamental to engineering because it dictates operational costs and environmental footprint. Improving efficiency reduces waste, allows for smaller cooling systems, and maximizes the utility derived from finite energy resources.
Avoid these traps
Common Mistakes
- Inverting output/input.
- Forgetting ×100.
- Getting efficiency > 100%.
One free problem
Practice Problem
An industrial electric motor consumes 800 Watts of electrical power and produces 680 Watts of mechanical power. What is the efficiency of the motor?
Solve for:
Hint: Divide the useful output power by the total input power and multiply the result by 100.
The full worked solution stays in the interactive walkthrough.
References
Sources
- Halliday, David, Resnick, Robert, Walker, Jearl. Fundamentals of Physics.
- Bird, R. Byron, Stewart, Warren E., Lightfoot, Edwin N. Transport Phenomena.
- Incropera, Frank P., DeWitt, David P., Bergman, Theodore L., Lavine, Adrienne S. Fundamentals of Heat and Mass Transfer.
- Wikipedia: Energy conversion efficiency
- IUPAC Gold Book
- AQA GCSE Physics
- Britannica
- Halliday, Resnick, and Walker, Fundamentals of Physics