A three-phase motor has a rated output of 7.5 kW and input of 9 kW. What is its efficiency?

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Study for the Ontario Power Generation (OPG) Orange 1 Test. Ace your exam with multiple choice questions and detailed explanations. Prepare confidently!

Multiple Choice

A three-phase motor has a rated output of 7.5 kW and input of 9 kW. What is its efficiency?

Explanation:
Efficiency is the fraction of input power that is converted into useful output power. Here, the motor delivers 7.5 kW of output from an input of 9 kW. So efficiency = 7.5 ÷ 9 = 0.8333..., which is 83.33%. Rounding to one decimal place gives 83.3%. The remaining power is lost to losses like heat and iron/friction losses, which is why the efficiency is less than 100%. If the efficiency were 75% or 70% or 90%, the corresponding output powers would be 6.75 kW, 6.3 kW, or 8.1 kW respectively, which doesn’t match the given output.

Efficiency is the fraction of input power that is converted into useful output power. Here, the motor delivers 7.5 kW of output from an input of 9 kW. So efficiency = 7.5 ÷ 9 = 0.8333..., which is 83.33%. Rounding to one decimal place gives 83.3%. The remaining power is lost to losses like heat and iron/friction losses, which is why the efficiency is less than 100%. If the efficiency were 75% or 70% or 90%, the corresponding output powers would be 6.75 kW, 6.3 kW, or 8.1 kW respectively, which doesn’t match the given output.

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