| Intermediate Technology Education | Energy and Power Technology | Pre-Design | Topic 3 | Activity 1 |
Efficiency
- Learn that energy can be saved by using more efficient appliances and systems
- Measure the work input to a system
- Measure the work output of that system
- Calculate the efficiency of the system
Efficiency
Have you replaced any of the older, incandescent (Edison) light blubs with the newer compact fluorescent lamps (CFL)? Many households are converting. But why? Usually there are two reasons given. First the CF lamps last up to 10 times as long, and second, they use much less energy. In fact a CF lamp uses less then a quarter of the energy of a traditional Edison bulb. With electricity costs for lighting making up to 25% of the monthly energy bill, it is obvious that you will save money.
Figure. Energy Star Logo
If you see this symbol on an appliance, computer, entertainment device, or any other product that uses energy, you are guaranteed that it uses 10 to 50 percent less energy than similar devices that don't qualify to use the logo.
Efficiency of a System
Simply stated, the efficiency of a system is related to how well it makes use of the energy it has at its disposal. No system is perfectly efficient. That is, of the energy input, some is always transformed into other types which is probably not the prime function of the system. For example,
A traditional incandescent lamp is a fairly efficient heater but a very inefficient light. That is because 95% of the energy used by the lamp is converted to heat and only 5% to its prime function, which is light.
Most often, the efficiency of a system is calculated as a ratio of the useful work output compared to the work input. Remember work and energy are really the same, energy being the ability to do work.
Efficiency of an Electric Motor
In the activity, you will investigate how well a small electric motor uses electricity. Motors are used to move things. Since they must use a force to move an object we can calculate the work done by the motor on the object (work output) using the classic definition of work:
Work Output = Force × Distance
Since a motor is an electrical device, the work input is really the electrical energy used by the motor to move the object. The electrical energy of the motor can be calculated by using a traditional formula (the same way the power company calculates the energy used at home)
Work Input = Voltage × Current × Time
Before we begin the activity let's review the units of measurement for each of the factors of the two formulas above.
| Factor | Unit | How is it Measured? |
|---|---|---|
| Force | Newton | Spring scale |
| Distance | Meter | Ruler or meter stick |
| Voltage | Volt | Voltmeter |
| Current | Ampere | Ammeter |
| Time | Second | Stop Watch |
For More information
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