Light bulb temperature variation

[BananaMan]

as part of a physics practical write up i have to measure the temperature of a light bulb envelopes temperature as the voltage increases.

first ... am i right in thinking a type J exposed thermocouple would do the trick for this?

if so, i heard something about one end being cold, to maintain a constant pd ?


second (most importantly)...am i right in thinking that a graph of V against Temp would be a straight line not through the origin?

thank you :)

p.s. already looked on the net for this and rly can't find n e thing on either point :S

 

[Chi Meson]

as part of a physics practical write up i have to measure the temperature of a light bulb envelopes temperature as the voltage increases.

first ... am i right in thinking a type J exposed thermocouple would do the trick for this?
if so, i heard something about one end being cold, to maintain a constant pd ?


second (most importantly)...am i right in thinking that a graph of V against Temp would be a straight line not through the origin?

thank you :)

p.s. already looked on the net for this and rly can't find n e thing on either point :S

A thermocouple would work, as would a thermistor (thermistors don't need a constant cold side).

Since the filament of a bulb will increase in resistance with temperature, and temperature will be proportional to the square of the current which will be proportional to the voltage and inversely proportional to the resistance which is proportional to the temperature... well, let's say that it might not be a straight line.

EDIT: correction, the power is proportional to the square of the current; the temperature depends on other factors including the rate of heat radiation which is proportional to the surface area of the filament as well as the difference in temperature between the filament and its surroundings. It's looking even less like a straight line graph now.

Antother point to consider, is that the "heat" energy that is carried away from the filament wil be increasingly in the form of infrared radiation. For things that are glowing, a more accurate reading of temperature is found by determining the peak wavelength of the output light. If you have not ecountered the Stefan-Boltzmann Law or "Blackbody radiation" then this is not the way to go.

 

[M98Ranger]

Yes, you are correct in thinking that a type J exposed thermocouple would be suitable for measuring the temperature of a light bulb envelope. This type of thermocouple is commonly used for temperature measurements in various industries, including the lighting industry.

As for the second point, the graph of voltage (V) against temperature would not be a straight line through the origin. This is because the resistance of the filament in the light bulb changes as the temperature increases, which affects the voltage across the bulb. Therefore, the relationship between voltage and temperature would not be linear and the graph would not go through the origin.

To accurately measure the temperature of the light bulb envelope, it is important to use a thermocouple that has been properly calibrated and has a known sensitivity to temperature. This will ensure that the measurements are accurate and reliable.

I hope this helps with your physics practical write-up. Good luck with your experiment!