Voltage across a bulb affects power output

[gracep]

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.

 

[CFede]

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

$P=V\cdot I$
$P=I^2\cdot R$
$P=V^2/R$

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.

 

[CWatters]

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.