Efficiency equals useful energy output over total input

Steps:

• Identify total energy input as E.
• Note wasted energy as Q, so useful energy is E - Q.
• Define efficiency as useful energy divided by total energy: (E - Q)/E.
• Simplify the expression: (E - Q)/E = 1 - Q/E.

Why C is correct:

• Efficiency is defined as the ratio of useful work output to total energy input, which algebraically equals 1 minus the wasted energy fraction (Q/E).

Why the others are wrong:

• A: This is the fraction of energy wasted, the opposite of efficiency.
• B: This expands to 1 - Q/E but is not the simplified form given in C.
• D: This incorrectly divides (1 - Q) by E, yielding a nonsensical fraction less than 1/E.

Final answer: C