Efficiency
Efficiency
Even though energy is conserved in an energy conversion process, the output of useful energy or work will be less than the energy input. The efficiency\(\text{Eff}\) of an energy conversion process is defined as
The table below lists some efficiencies of mechanical devices and human activities. In a coal-fired power plant, for example, about 40% of the chemical energy in the coal becomes useful electrical energy. The other 60% transforms into other (perhaps less useful) energy forms, such as thermal energy, which is then released to the environment through combustion gases and cooling towers.
Efficiency of the Human Body and Mechanical Devices
| Activity/device | Efficiency (%) |
|---|---|
| Cycling and climbing | 20 |
| Swimming, surface | 2 |
| Swimming, submerged | 4 |
| Shoveling | 3 |
| Weightlifting | 9 |
| Steam engine | 17 |
| Gasoline engine | 30 |
| Diesel engine | 35 |
| Nuclear power plant | 35 |
| Coal power plant | 42 |
| Electric motor | 98 |
| Compact fluorescent light | 20 |
| Gas heater (residential) | 90 |
| Solar cell | 10 |
PhET Explorations: Masses and Springs
A realistic mass and spring laboratory. Hang masses from springs and adjust the spring stiffness and damping. You can even slow time. Transport the lab to different planets. A chart shows the kinetic, potential, and thermal energies for each spring.
This lesson is part of:
Work, Energy and Energy Resources