Table 1.1 shows the power rating and efficiency of four electric motors. Which motor provides the greatest useful output power? motor input power / W effici...
Question 1 Report
Table 1.1 shows the power rating and efficiency of four electric motors. Which motor provides the greatest useful output power?
| motor | input power / W | efficiency / % |
|---|---|---|
| P | 200 | 90 |
| Q | 500 | 40 |
| R | 300 | 60 |
| S | 150 | 80 |
Answer Details
Useful output power equals the input power multiplied by the efficiency (expressed as a decimal):
\[ P_{\text{useful}} = P_{\text{input}} \times \text{efficiency} \]
- Motor P: \( 200 \times 0.90 = 180 \text{ W} \)
- Motor Q: \( 500 \times 0.40 = 200 \text{ W} \)
- Motor R: \( 300 \times 0.60 = 180 \text{ W} \)
- Motor S: \( 150 \times 0.80 = 120 \text{ W} \)
Motor Q provides the greatest useful output power at 200 W, despite having the lowest efficiency. A high input power can compensate for low efficiency. This illustrates why both the power rating and the efficiency must be considered together when determining useful output.
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