Efficiency Formula for Energy Transfers

Steps:

• Recall that efficiency measures how much input energy becomes useful output.
• Identify the standard formula: efficiency equals useful energy out divided by total energy in, often as a percentage.
• Compare choices to this formula, checking numerator and denominator.
• Select the option matching the definition exactly.

Why A is correct:

• It directly matches the physics definition of efficiency as the ratio of useful output energy to total input energy, per conservation of energy principles.

Why the others are wrong:

• B simplifies to 1 (or 100%), ignoring losses and not measuring efficiency.
• C uses a partial output, underestimating true efficiency by excluding all input.
• D focuses only on converted energy, not the full useful output relative to input.

Final answer: A