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Electronics => Beginners => Topic started by: Simon123 on March 11, 2014, 03:56:36 pm

Title: Temperature of lightbulb tungsten wire
Post by: Simon123 on March 11, 2014, 03:56:36 pm
Hello!

In school we had to calculate temperatur of lb tungsten from data we collected druing measurments.
The formula we were given is R=R20(resistance at 20°c)+R20*a(temperature coeficient)*change in temperature.
I rearanged formula like this:
?T=(R-R20)/(R20*a)
Is this correct?
Title: Re: Temperature of lightbulb tungsten wire
Post by: Len on March 11, 2014, 04:10:40 pm
Maybe. Does "?T" mean "change in temperature"?
Title: Re: Temperature of lightbulb tungsten wire
Post by: Simon123 on March 11, 2014, 04:24:04 pm
Yea, sorry i inserted delta symbol and it converted it into this.
Title: Re: Temperature of lightbulb tungsten wire
Post by: Len on March 11, 2014, 04:41:39 pm
Quote from: Simon123 on March 11, 2014, 04:24:04 pm
Yea, sorry i inserted delta symbol and it converted it into this.
Yes, it looks correct to me.
Title: Re: Temperature of lightbulb tungsten wire
Post by: Simon123 on March 11, 2014, 05:02:08 pm
Ok, thanks.
Title: Re: Temperature of lightbulb tungsten wire
Post by: IanB on March 11, 2014, 05:16:39 pm
Given:

R = R20 + R20 · a · (T - 20)

You can factorize this:

R = R20 [ 1 + a (T - 20) ]

Do you now see a better way to rearrange it?

Title: Re: Temperature of lightbulb tungsten wire
Post by: tszaboo on March 11, 2014, 10:22:24 pm
Hint: It will be around 6000 K to match the color of the sun, unless you tweaked the voltage.
You are right, it is getting late.
Title: Re: Temperature of lightbulb tungsten wire
Post by: Len on March 11, 2014, 10:55:25 pm
Quote from: NANDBlog on March 11, 2014, 10:22:24 pm
Hint: It will be around 6000 K to match the color of the sun, unless you tweaked the voltage.
That turns out not to be the case. Tungsten incandescent bulbs are not the same colour as sunlight. You can see this if you turn on a light during the day.
Title: Re: Temperature of lightbulb tungsten wire
Post by: ConKbot on March 11, 2014, 11:56:47 pm
Quote from: Len on March 11, 2014, 10:55:25 pm
Quote from: NANDBlog on March 11, 2014, 10:22:24 pm
Hint: It will be around 6000 K to match the color of the sun, unless you tweaked the voltage.
That turns out not to be the case. Tungsten incandescent bulbs are not the same colour as sunlight. You can see this if you turn on a light during the day.

Traditional incandescent bulbs should be in the 2500-3000K range, and a halogen bulbs run hotter in the 3000K to 4000K range, however thats ideally, assuming the emissions are black-body, which they probably arent exactly, but it should get you in the right ballpark at least.