Researchers have developed a new type of filament lamp with an efficiency of 40%. Old-type filament lamps have an efficiency of 5.0%. The two types of lamp produce the same useful output power.
What is the ratio
input power to new type of lamp / input power to old type of lamp?
A 0.13
B 0.63
C 1.6
D 8.0
ANSWER: A
The Physics Behind
- Efficiency e is
e = useful power / input power.
input power = useful power / e
- The ratio r which is input power to new type of lamp / input power to old type of lamp therefore is
r = (useful power / 0.4) ÷ (useful power / 0.05)
r = 0.05 / 0.4 because useful power is the same
r = 0.125
r = 0.13
[rounded off to following the proper number of significant figures]
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