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Guess The Efficiency
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Guess The Efficiency

Credit: James Bowe
Source: http://www.flickr.com/photos/jamesrbowe/3338776771/
License: CC BY-NC 3.0

Thomas Edison created the first practical incandescent light bulb in 1878. Since then the light bulb has permanently changed the way the human world lives. Despite technological improvements on material and shape, the modern light bulb remains highly inefficient. 

News You Can Use

  • Regular incandescent light bulbs convert electrical energy into heat and light which is then radiated through the glass while the heat raises the temperature of the bulb. By performing a simple experiment that measures the rate at which the thermal energy (Pheat)  is given off and the total heat energy of the light bulb (Ptotal), one can determine the efficiency using the following equation:

 \varepsilon=\frac{P_{total}-P_{heat}}{P_{total}}

  • Surprisingly, the efficiency of most light bulbs ranges from 8 to 10%. When compared to other light bulbs, incandescent light bulbs produce the most heat and are extremely inefficient compared to other types that are currently available. Unfortunately for the environment, they are still widely used due to their low purchase price. 
  • Recent laws have been passed to slowly phase out some of the most common incandescent light bulbs by 2014. These bulbs will be replaced with longer lasting, more energy efficient light bulbs. While these newer bulbs are more expensive to purchase, their longer life and lower power drain will ultimately cost individuals less in the long run.
  • Watch how a light bulb is made:

http://www.youtube.com/watch?v=BylLOWRojyY

Show What You Learned

Using the information provided above, answer the following questions.

  1. What is the benefit of coating the filament in the light bulb?
  2. How does filling an incandescent light bulb with an inert gas extend the life of the light bulb?
  3. The electrical current heats the filament to temperatures in the range of 2,000 ? 3,000 Kelvin. Given this information, what would you expect the melting point of tungsten to be?

Image Attributions

  1. [1]^ Credit: James Bowe; Source: http://www.flickr.com/photos/jamesrbowe/3338776771/; License: CC BY-NC 3.0

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