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Home Q & A Board Science-Related Homework Help Physics
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retard23 retard23
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5 years ago
Compact fluorescent bulbs typically last 10 years while incandescent bulbs last about 1 year.
 
  For a given amount of light, a tungsten bulb draws 100 W and a compact
  fluorescent bulb draws 15 W. If the cost of electricity is 0.10/kWh, how long would you
  have to operate a compact fluorescent bulb to save 5.00 compared to the costs of operating
  a tungsten bulb?
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jester1997!jester1997!
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5 years ago
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Let's look at this in terms of yearly operating cost. At 0.10/kWh the tungsten
bulb will draw energy in the amount 100 W x T x 0.10/kWh = 0.01/h x T. The compact
fluorescent will draw energy in the amount 15 W x T x 0.10/kWh = 0.0015/h x T. We
would look for 5.00 + 0.0015/h x T = 0.01/h x T. This is solved by gathering terms:
0.01/h x T - 0.0015/h x T = 0.0085/h x T = 5.00
or
T = 5.00/0.0085/h = 588.2 h.
If we factor in the bulb costs, we'd modify this to
5.00 + 1.00 + 0.0015/h x T = 0.50 + 0.01/h x T.
In this case,
T = 5.50/0.0085/h = 647.1 h.
1

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