Reference no: EM131426344

Objectives:

This experiment was designed to examine the different aspects of radiation. That is done by testing two different concepts, Stefan-Boltzmann low and the radiant emissivity of various materials.

Introduction

According to thermodynamics, thermal radiation is the electromagnetic radiation emitted by a body as a result of its temperature [1]. What is of interest in this lab, however, is that the thermal radiation emitted by different objects at the same temperature can be of different values, although this is not always immediately obvious.

The purpose of this lab will be to show quantitatively that the radiation. emitted by four different surfaces is not equal to each other materials ohmmeter, millivolt meter, thermal radiation cube, radiation Sensor, westward Infrared Thermometer.The procedure can be found in Lab Manual. After taking themeasurementswith the radiation sensor, whereas the radiation sensor gave a value in units of millivolts. This was the only addendum to the

Results

From the results it can be seen with relative ease that the radiation emitted by a surface being warmed by the same light bulb is not the same. The ohmmeter was allowed to reach thermal equilibrium in each of the above cases, yet the sides did not match up in temperature, hence they were not emitting the same amount of thermal radiation.

Discussion

Although each of the four surfaces of the cube (polished aluminum, dull aluminum, white, and black were exposed to the same heat  source for the same amount of time, the sides did not emit the same amount of thermal radiation, meaning they did not have the same temperature.

It is not immediately obvious why different surfaces exposed to the same amount of thermal radiation will not have the same  temperature. However, if you think of a mirror, for a moment, what is a mirror's purpose? To reflect light; So by extension, it should reflect thermal radiation to at least some degree. Thus, it will not get quite as hot as something that does not reflect light. However, everything reflects radiation to some degree; it just comes down to a matter of  how much.

Albedo is what best describes how much radiation a surface reflects. Something with a high albedo will reflect more radiation than a surface with a small albedo. Thus, if two surfaces are exposed to the same amount of radiation for the same amount of time, the surface with the highest albedo will have the lowest temperature. This is confirmed by the data as the polished aluminum side of the radiation cube is approximately a mirror (it has a very high reflexivity).

One paradox inherent in the above data is that in every trial, the white side of the cube is warmer is than the black side of the cube. White would seem to have a higher albedo, thus reflecting more thermal energy, though that does not seem to be the case. Instead, since the object is white, that means it is absorbing radiation of all visible light, and then must be absorbing more thermal radiation than the black side. Black is the lack of color, so thus it is not absorbing any radiation of the visible wavelength. This may not in fact be the case, though it is an adequate explanation for the observed number.

Conclusion

Different materials exposed to the same heat source for the same amount of time will not come to the same temperature. It is not immediately obvious from the experiment why this is. This experiment opens up an odd paradox of thermal radiation. Why is the white hotter than the black? How can this be explained?