Engineering Board Exam Reviewer · Energy and Power · hard
A 100 W and a 40 W lamp, both rated 120 V, are connected in series across 120 V. How much power does the 40 W lamp dissipate (assume fixed resistances)?
- 20.41 W
- 8.16 W
- 40 W
- 28.57 W
Answer
A. 20.41 W
Solution
R100=1202/100=144, and R40=1202/40=360, . I=120/144+360=0.238 A. P40=I2(360)=20.41 W (the 100 W lamp gets only 8.16 W, so the dimmer-rated lamp is brighter in series).
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