Question

If Star 1 emits more electromagnetic radiation per unit area per unit time than Star 2, we can conclude that:

1. the stars may have the same temperatures, depending on their chemical compositions.
2. Star 1 is at a higher temperature.
3. Star 2 is at a higher temperature.
4. the stars may have the same temperatures, depending on their relative sizes.

It was found that the amount of radiation emitted by Surface 1 of the thermal radiation cube is greater than that emitted by Surface 2, when the temperature of both surfaces is 2500 K. If the surface temperature of both surface is then decreased to 1500 K, the amount of radiation emitted by Surface 1:

1. will be the same as that emitted by Surface 2.
2. may be either greater or smaller than that emitted by Surface 2.
3. will be smaller than that emitted by Surface 2.
4. will be greater than that emitted by Surface 2.

In reference to the same two surfaces as in the previous question, we can conclude that Surface 1 is a:

1. better absorber of radiation than Surface 2.
2. poorer absorber of radiation than Surface 2.
3. poorer absorber than Surface 2 at higher temperatures, but better at lower temperatures.
4. better absorber than Surface 2 at higher temperatures, but poorer at lower temperatures.

(Refer to Appendix B of the lab handout) It was found that the relative resistance of a filament is 14.12. We can conclude that the filament's temperature is about:

1. 72^o C
2. 2650 K
3. 79 K
4. 2650^o C

In this lab, you should get that the coefficient next to T⁴ in the Rad T⁴ graph:

1. is both numerically equal (within the experimental error) to and has the same unit as σ.
2. is numerically different from σ, but has the same unit.
3. is numerically equal to (within the experimental error) Stefan-Boltzmann constant, σ, but has different unit than σ.
4. is neither numerically equal to, nor does it have the same unit as σ.

Answer 1

1. According to Stefan Boltzmann law we have

$E/A=\sigma T^4$

This implies higher radiation per unit area higher the temperature.

So, star 1 has higher temperature.

2. Of a radiation cube surface 1 emits more photons at higher temperature than surface 2 i.e. it has color that matches that of low temperature but surface 1 has color corresponding to that of high temperature wavelength which absorbs radiation of high temperature photons.

When temperature is lowered the radiation will get absorbed more by surface 1 and hence emitted photons will be smaller compare to surface 2.

3.

As explained above surface 1 is bad absorber at high temperature and a good absorber at low temperature.