Studying Emissivity Effects on a Copper Box Experiment"

[Sleve123]

Homework Statement

The experiment we did was pretty basic, it was a copper box with five different metal rods (unlagged and of equal lengths and diameter) welded onto the bottom, on the bottom of each were pins stuck with petroleum jelly. Hot water was then added to the box and the order at which the pins dropped recorded.

I was wondering if the emissivity of the surface of the metal rods would have any major affects on the order, for example a metal may have a high emissivity and high k value (thermal conductivity) and may take longer than a low emissivity low k value metal rod. Giving you the impression that the first rod has a lower k value than the second, if you were to assume the time taken is only related to the k value of the metal.

 

[Andrew Mason]

I was wondering if the emissivity of the surface of the metal rods would have any major affects on the order, for example a metal may have a high emissivity and high k value (thermal conductivity) and may take longer than a low emissivity low k value metal rod. Giving you the impression that the first rod has a lower k value than the second, if you were to assume the time taken is only related to the k value of the metal.

Emissivity is not a factor. You can calculate the energy lost by radiation due to the temperature difference between the rod and the surroundings over a broad range of possible emissivities (ie. apply the Stefan-Boltzmann law $P = A\epsilon\sigma T^4$) You will see that the amount of energy lost by radiation is insignificant.

AM