Question

How do you calculate the efficiency of an electrical device?

Answer 1

The efficiency of an electrical device can be calculated using the formula:

\[
\text{Efficiency} (\%) = \left( \frac{\text{Output Power}}{\text{Input Power}} \right) \times 100
\]

1. **Input Power**: This is the total power supplied to the device, typically measured in watts (W).
2. **Output Power**: This is the useful power output by the device, also measured in watts.

For example, if an electrical device has an input power of 100 W and an output power of 80 W, the efficiency would be:

\[
\text{Efficiency} = \left( \frac{80}{100} \right) \times 100 = 80\%
\]

This means the device converts 80% of the input power into useful work, with the remainder lost as heat or other forms of energy.

Answer 2

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.