ASSIGNMENT
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?
