Why filament intensity profile of filament lamp deviates from blackboady curve?

In summary, the intensity profile of a filament lamp can deviate from a blackbody curve due to the presence of different elements with their own unique emission lines and other factors such as temperature and pressure. This phenomenon is also observed in stars, where their emission profiles can also deviate from smooth curves due to the elements they are made of.
  • #1
AStaunton
105
1
doing experiment today in which the intensity profile of a filament lamp (of surface temp around 2000K I think) is studied by passing it through a rotating grating apparatus and then reading the output from oscilloscope.

My question is why the intensity profile intensity profile the osc.scope displayed deviated so markedly from a blackbody curve (I think the filament is to a good approx a blackbody). Although it did resemble a blackbody curve, it was not as close a fit as I would have thought. The only reason I can think of is it is for the same reason that stars emission profile also deviates, ie the elements that the body is made of impose their characteristic emission lines on the curve and so the actual curve is more jagged than it otherwise would be.

Can someone please confirm this or correct me on this issue?
 
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  • #2


I can confirm that your reasoning is correct. The reason for the deviation in the intensity profile of the filament lamp from a blackbody curve is due to the elements that make up the filament. A blackbody curve represents the ideal emission spectrum of an object at a given temperature, with a smooth and continuous distribution of energy across all wavelengths. However, real objects, including the filament in a lamp, are made up of different elements that have their own characteristic emission lines. These emission lines can add to or subtract from the overall intensity at certain wavelengths, resulting in a jagged or deviated intensity profile. This phenomenon is known as spectral lines or emission lines.

In the case of a filament lamp, the filament is usually made of tungsten, which has its own unique emission lines. These emission lines can be seen as small dips or peaks in the intensity profile, causing it to deviate from a smooth blackbody curve. This is similar to how different elements in stars can affect their emission profiles, resulting in a jagged or deviated curve.

In addition, other factors such as the temperature and pressure of the filament can also contribute to the deviation from a blackbody curve. Overall, the deviation in the intensity profile of the filament lamp is a result of the complex interactions between the elements that make up the filament and the conditions under which it is emitting light.

I hope this clarifies your question. Keep up the good work in your experiments!
 

1. Why does the filament intensity profile of a filament lamp deviate from the blackbody curve?

The filament intensity profile of a filament lamp deviates from the blackbody curve due to several factors. First, the filament of a lamp is made of a material with a specific melting point, which limits the maximum temperature it can reach. This results in a lower peak intensity compared to a true blackbody radiator, which has no such limitation. Additionally, the filament is not a perfect emitter, as it reflects some of the radiation back into the lamp, further decreasing the intensity. Finally, the shape and structure of the filament also contribute to the deviation from the blackbody curve.

2. Does the deviation from the blackbody curve affect the performance of a filament lamp?

Yes, the deviation from the blackbody curve can affect the performance of a filament lamp. The lower peak intensity means that the lamp produces less light compared to a perfect blackbody radiator. This can result in a lower brightness and a decrease in the efficiency of the lamp. Additionally, the deviation can also affect the color temperature of the light emitted, making it appear slightly warmer or cooler than the ideal blackbody radiation.

3. Can the deviation from the blackbody curve be corrected?

Yes, the deviation from the blackbody curve can be corrected to some extent. One way to achieve this is by using a different filament material with a higher melting point, which can increase the peak intensity of the lamp. Another method is to use a reflecting coating on the inner surface of the lamp to reduce the amount of radiation reflected back into the lamp. However, it is almost impossible to completely eliminate the deviation and achieve a perfect blackbody curve.

4. How does the temperature of the filament affect the deviation from the blackbody curve?

The temperature of the filament plays a crucial role in the deviation from the blackbody curve. As the temperature increases, the peak intensity also increases, resulting in a closer alignment with the blackbody curve. However, the filament's melting point limits the maximum temperature it can reach, so increasing the temperature can only reduce the deviation to a certain extent.

5. Are there any other types of lamps that produce a closer approximation to the blackbody curve?

Yes, there are other types of lamps that produce a closer approximation to the blackbody curve. One example is the gas discharge lamp, which uses noble gases and metal vapors to produce light. These lamps can have a higher peak intensity and a more uniform spectral distribution, resulting in a closer alignment with the blackbody curve. However, they also have their own limitations and are not perfect blackbody radiators.

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