Thermal radiation lab experiment

[subzero0137]

Hi,

I have to plan and carry out an experiment on thermal radiation as part of my physics lab module. The description of the experiment is as follows: Investigate the radiation from a bulb filament as a function of input power, using a pyrometer to measure the temperature of the filament.

I'm guessing the purpose of this experiment is to verify the Stefan-Boltzmann law, which states that P=AσT^4 where P is the power radiated from the object, A is the surface area of the object (filament or light bulb?) and T is its temperature in Kelvin, and σ is the Stefan-Boltzmann constant. So, plotting P against T^4, and dividing the gradient of the resultant graph by A should give me a value close to Stefan's constant. But I have 2 questions:

1) Should I measure the surface area of the bulb, or the filament?
2) Can I assume input power = P, so that I can calculate the values of P using a multimeter in a circuit?

Any ideas would be appreciated.

 

[haruspex]

1) Should I measure the surface area of the bulb, or the filament?

If you kept the filament the same but made the bulb ten times the diameter, would the power from it change?

2) Can I assume input power = P, so that I can calculate the values of P using a multimeter in a circuit?

Seems fair.

 

[subzero0137]

If you kept the filament the same but made the bulb ten times the diameter, would the power from it change?

I don't think it would.

 

[haruspex]

I don't think it would.

Right, so which area matters?

 

[subzero0137]

Right, so which area matters?

The surface area of the filament.

 

[haruspex]

The surface area of the filament.

Yes.