Exam-style question
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If a transformer has an efficiency of 90% and the input power is 1000 W, what is the useful output power?.
- A.900 W
- B.950 W
- C.1000 W
- D.1100 W
Model answer
What a good answer should say
- 900 W
Explanation
Why this works
Using the efficiency formula: efficiency = (useful output / total input) x 100, we can rearrange to find useful output: useful output = efficiency x total input / 100. Substituting the values, useful output = 90% x 1000 W / 100 = 900 W.
This indicates the effective power delivered by the transformer.
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