Unformatted text preview: rescent lamp (CFL) produces 1839 lumens of light. What is the efficacy of the CFL (in lumens/watt)? Correct C ) 61.3 lumens/watt Efficacy = 1839/30 = 61.3 lumens/watt A 100 watt incandescent light bulb is operated for 11 hours, and a 32 watt fluorescent light bulb is operated for the same period of time. At 8 cents per kWh, what is the cost savings in using the fluorescent bulb? Correct B ) 0.06 Incandescent light bulb Energy consumed = 100/1000 x 11 = 1.1 kWh Energy Cost = 1.1 x 8/100 = $0.088 Fluorescent light bulb Energy consumed = 32/1000 x 11 = 0.352 kWh Energy Cost = 0.352 x 8/100 = $0.02816 Savings in Energy Cost = 0.088 0.02816 = $0.05984 A 75 watt light bulb produces 5 watts of radiant energy and 70 watts of heat energy. What is its efficiency? Correct A ) 0.0667 Efficiency = 5/75 = 0.0667 Heather is a smart person who wants to save energy and money. So, she has replaced the 120 Watt incandescent light bulb in her house with a 28 Watt CFL bulb. The expected life of incandescent and CFL bulbs is 800 h and 8000 hours respectively. The purchase price of an incandescent bulb is $0.67 and for the CFL it is $5.71. The cost of electricity is 7 cents per kWh. What is her total savings over the life of the CFL bulb? Correct A ) 52.51 CFL energy cost for 8000 hrs = 28 / 1000 x 8000 x 7/100 = $15.68 Total cost for CFL = 5.71 + 15.68 = $21.39 Incandescent light energy cost for 8000 hrs = 120/ 1000 x 8000 x 7/100 = $67.2 # of Incandescent bulbs required = 8000/800 = 10 bulbs Total cost for Incandescent light = (0.67 x 10) + 67.2 = $73.9 Total Savings = 73.9 21.39 = $52.51 The kitchen in your house measures 5 ft by 11 ft. You need to have 50 footcandles of illumination in the room. How many 75 watt bulbs will be required if one bulb emits 1375 lumens. (1 footcandle = 1 lumen/sq.ft) Correct A ) 2 bulbs Area of the room = 5 x 11 = 55 sq.ft Lumens required = 50 x 55 = 2750 lumens # of bulbs required = 2750/1375 = 2 bulbs For an Incandescent bulb, initial cost may be high but the energy costs will be low over its life time. C...
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 Spring '07
 PISUPATI,SARMAVE
 Energy, Light, Incandescent light bulb, CFL

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