Lamp efficiency uses useful power over total input power ratio

Steps:

• Total input power to lamp = 60 W (energy transfer rate).
• Wasted power = 46 W.
• Useful output power = 60 W - 46 W = 14 W.
• Efficiency ratio = useful output / total input = 14/60.

Why B is correct:

• Efficiency formula is (useful power / total input power) × 100%, so ratio 14/60 matches B.

Why the others are wrong:

• A: 14/74 incorrectly adds extra power to total.
• C: 14/46 divides useful by wasted power, irrelevant to efficiency.
• D: 60/60 equals 1, ignores useful output.

Final answer: B