Efficiency Measures Useful Output Over Total Input

Steps:

• Recall that efficiency in a system quantifies how much input energy becomes useful output.
• Identify the standard formula: efficiency = (useful energy output / total energy input) × 100%.
• Evaluate choices by matching them to this formula.
• Select the option that directly represents the ratio of useful output to total input.

Why C is correct:

• It matches the physics definition of efficiency as the fraction of total energy input converted to useful energy output.

Why the others are wrong:

• A inverts the ratio, giving the reciprocal of efficiency.
• B adds outputs incorrectly and uses wrong input term, not matching any standard formula.
• D confuses total output with input and uses nonexistent "wasted energy input."

Final answer: C