To calculate the efficiency of an electrical device, you use the following formula:
\[ \text{Efficiency} (\%) = \left( \frac{\text{Output Power}}{\text{Input Power}} \right) \times 100 \]
Here’s a step-by-step guide on how to apply this formula:
1. **Determine the Input Power**: Measure or find out the total power supplied to the device. This is usually given in watts (W).
2. **Determine the Output Power**: Measure or find out the useful power output by the device. This is also usually given in watts (W).
3. **Apply the Efficiency Formula**: Plug the values of input power and output power into the formula.
### Example
Let's say you have an electric motor with an input power of 1000 watts and an output power of 800 watts. To find the efficiency:
1. **Input Power** = 1000 W
2. **Output Power** = 800 W
Using the formula:
\[ \text{Efficiency} (\%) = \left( \frac{800}{1000} \right) \times 100 = 80\% \]
So, the efficiency of the motor is 80%.
### Key Points to Remember
- **Efficiency** is always a percentage and indicates how well the device converts input power into useful output power.
- In practical scenarios, some power is lost due to factors like heat, friction, or other forms of energy dissipation, which is why efficiency is typically less than 100%.
- For devices like transformers or generators, output power might be measured in terms of real work done, such as lifting a weight or moving a load.