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Diffstat (limited to 'blackbody_new.tex')
| -rw-r--r-- | blackbody_new.tex | 2 |
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diff --git a/blackbody_new.tex b/blackbody_new.tex index 8a72e51..c3bf73d 100644 --- a/blackbody_new.tex +++ b/blackbody_new.tex @@ -152,7 +152,7 @@ Before starting actual experiment take some time to have fun with the thermal ra In the lab report plot the reading from the radiation sensor (convert to $W/m^2$) (on the y axis) versus the temperature $T^4$ on the x axis. According to the Stefan-Boltzmann Law, the data should show a linear dependence, since according to Eq.(\ref{SBl}) $S\propto T^4$. Fit the experimental data using a linear fit and its uncertainty. For an ideal blackbody we expect the slope to be equal to the Stephen constant $\sigma=5.6703 \times 10^{-8} W/m^2K^4$. However, there exists no ideal black bodies. For real objects the Eq.(\ref{SBl}) is modified, and written as: -\begin{equation}\label{SBl} +\begin{equation}\label{SBlmod} S =\epsilon\sigma T^4 \end{equation} where the coefficient $\epsilon$ is called \emph{emissivity} and is defined as the ratio of the energy radiated from a material's surface to that radiated by a perfect blackbody at the same temperature. The values of $\epsilon$ vary from 0 to 1, with one corresponding to an ideal blackbody. All real materials have $\epsilon<1$, although some come quite close to the ideal (for example, carbon black has $\epsilon=0.95$). However, emissivity of a tungsten wire varies from $\epsilon=0.032$ (at $30^{\circ} C$) to $\epsilon=0.35$ (at $3300^{\circ}C$). Using the result of your fit, and assuming we know the Stephan-Boltzman constant $\sigma$ by some other means, what is $\epsilon$ and what is the uncertainty on it? Is it consistent with tungsten? What else could be affecting this measurement? |