Question

efficiency of machines quick check
which is the equation for a machine’s efficiency? (1 point)
○ efficiency = input energy + output energy
○ efficiency = \\(\frac{input energy}{output energy}\\) · 100
○ efficiency = \\(\frac{output energy}{input energy}\\) · 100
○ efficiency = input energy − output energy

Explanation:

To determine the equation for a machine's efficiency, we recall the concept: Efficiency measures how much of the input energy is converted into useful output energy. The formula is the ratio of output energy to input energy, multiplied by 100 to get a percentage.

• The first option (Efficiency = input energy + output energy) is incorrect as efficiency is a ratio, not a sum.
• The second option (Efficiency = (input energy / output energy) × 100) is incorrect because it inverts the ratio (we care about how much output we get from input, not vice versa).
• The third option (Efficiency = (output energy / input energy) × 100) is correct, as it takes the useful output energy relative to the input energy and expresses it as a percentage.
• The fourth option (Efficiency = input energy − output energy) is incorrect as efficiency is not a difference of energies.

Answer:

The correct option is the third one: $\boldsymbol{\text{Efficiency} = \frac{\text{output energy}}{\text{input energy}} \cdot 100}$ (the option with the blue dot and the formula $\text{Efficiency} = \frac{\text{output energy}}{\text{input energy}} \cdot 100$).