Light bulb

  • Thread starter _Muddy_
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  • #1
_Muddy_
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Homework Statement



We did an experiment in class abvout resistance and temperature. The teacher told us to find out why light bulbs usually blow when you turn on the light. It must be related to the experiment we did which was seeing how resistance changed with temperature

Homework Equations


I'm not sure if there are any, If there are please tell me


The Attempt at a Solution


I have no idea why, and i wouldn't know where to look on the internet

thanks

_Muddy_
 

Answers and Replies

  • #2
mgb_phys
Science Advisor
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The light bulb fails because the current through the filament is too large.
The current depends on the resistance
How does the resistance of metal change with temperature ?
 
  • #3
_Muddy_
17
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The light bulb fails because the current through the filament is too large.
The current depends on the resistance
How does the resistance of metal change with temperature ?

The higher the temperature the higher the resistance.

So then, the light bulb fails because the current through the filament is too large. The resistance is too low. So the temperature is too high. Is that correct? What actually happens to the filament, does it break? Why would a high temperature/ high current make the light bulb fail?
 
  • #4
mgb_phys
Science Advisor
Homework Helper
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The filament is a thin metal wire - rather like a fuse.
When the filament is cold the resistance is lower and so the currentis higher.

The current heats the wire which expands which puts a mechanical strain on it.
Also when the light is first turned on is the greatest temperature difference and so the greatest strain - this is probablyy more important than the resistance in reality
 
  • #5
_Muddy_
17
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thanks a lot for that, I'm pleased and my teacher should be pleased aswell
 

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