Lamp Efficiency Calculation

Steps:

• Identify useful energy output as light: 8 J.
• Calculate total energy input: thermal energy (92 J) + light energy (8 J) = 100 J.
• Apply efficiency formula: (light energy / total energy) × 100% = (8 / 100) × 100% = 8%.
• Express as percentage: 8%.

Why A is correct:

• Efficiency is defined as (useful output / total input) × 100%, yielding 8% for light conversion.

Why the others are wrong:

• B: 9% incorrectly assumes a different ratio or rounding error.
• C: 1% inverts the ratio, treating light as 1% of total.
• D: 92% mistakes thermal waste for useful light output.

Final answer: A