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Question:
Different designs for light bulbs: How is one light bulb created to be powered by a 6 volt battery while another light bulb can be designed to operated from 120 V ac? When you talk about light bulbs, do they respond differently to AC and Dc? If I say I have a 6V source of light, if I use 120V, will the filament melt?



Replies:
A light bulb filament glows because it is hot. The filament is hot because electrical power is heating it. The power is I- squared R. Can you now answer your own questions? By the way, one can vary R by varying the length and thickness of the filament. Have I left out anything that you need to answer your question?


The above answer will get you started. However, there are more variables in this problem than there are constants. For example, the material the filament is made of can greatly vary its resistance with the amount of heat (watts) that it dissipates. In addition, sealed bulbs generally are in a semi-vacuum that has some ionized gases in the area around it to help the filament to glow. That is why GE and Phillips gets big bucks for the designs of very efficient light bulbs. Years of materials research have gone on in the design of bulbs, and in recent years they have become considerably more efficient.



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