Voltage across a bulb affects power output

  • Thread starter gracep
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  • #1
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Homework Statement


I'm studying for my GCSE exam and I need to know how changing the voltage across a bulb affect it's power output for my secondary evidence, i have searched the internet for the answer but can't find anything. Anyone know how it affects it OR any useful websites to use? thankyou.


Homework Equations


P=VxI


The Attempt at a Solution


I have wrote that the bigger the voltage going into the bulb, the more the power output will be because P=VxI but I need to write more? thankyou.
 

Answers and Replies

  • #2
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Hi gracep. You can write 3 "different" recipes for the power output:

[itex]P=V\cdot I[/itex]
[itex]P=I^2\cdot R[/itex]
[itex]P=V^2/R[/itex]

These 3 things are all related through Ohm's Law.

What you need is something that relates voltage and power and where everything else in the equation is a constant.

So, it depends on the problem you have. If you have a constant intensity you would use the first relation. If you have a constant resistance (wich is probably the more common situation), then you want to use the third relation.

From that you can easily see how the power behaves when changing voltage.
 
  • #3
CWatters
Science Advisor
Homework Helper
Gold Member
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What he said..

Rather than mentioning P=IV, I would point out that the power is proportional to V2.

That's because increasing V also increases I. It would be so better to rearrange the equation given using Ohms Law...

Ohms Law..
V=IR
so
I=V/R

You were given P=IV so substitute for I giving

P=V2/R

Hence power is proportional to V2.

I supose you might get an extra mark for pointing out that R might not be constant. It might vary with temperature.
 

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