Question
Integrate Equation $34.3$ over all wavelengths to get the total power radiated per unit area. Show that your result is equivalent to Equation $34.1$, with the Stefan-Boltzmann constant given by $\sigma=2 \pi^{5} k^{4} / 15 c^{2} h^{3}$.
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3 Equation 34.3 is the Planck's radiation law, which gives the spectral radiance of a black body at temperature T: $B(\lambda, T) = \frac{2\pi hc^2}{\lambda^5} \frac{1}{e^{\frac{hc}{\lambda kT}} - 1}$ Show more…
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Integrate Equation 34.3 over all wavelengths to get the total power radiated per unit area. Show that your result is equivalent to Equation $34.1,$ with the Stefan-Boltzmann constant given by $\sigma=2 \pi^{5} k^{4} / 15 c^{2} h^{3} .$ (Hint: Use $h c / \lambda k T$ as the integration variable.)
(a) Integrate Eq. ( 27 ) over all wavelengths to obtain an expression for the total luminosity of a blackbody model star. Hint: $$\int_{0}^{\infty} \frac{u^{3} d u}{e^{u}-1}=\frac{\pi^{4}}{15}$$ $$=\frac{8 \pi^{2} R^{2} h c^{2} / \lambda^{5}}{e^{h c / \lambda k T}-1} d \lambda$$ (b) Compare your result with the Stefan-Boltzmann equation $(17),$ and show that the StefanBoltzmann constant $\sigma$ is given by $$\sigma=\frac{2 \pi^{5} k^{4}}{15 c^{2} h^{3}}$$ $$L=4 \pi R^{2} \sigma T_{e}^{4}$$ (c) Calculate the value of $\sigma$ from this expression.
Derive the Stefan-Boltzmann formula for the total energy density in blackbody radiation: $$ \frac{E}{V}=\left(\frac{\pi^{2} k_{B}^{4}}{15 \hbar^{3} c^{3}}\right) T^{4}=\left(7.57 \times 10^{-16} \mathrm{Jm}^{-3} \mathrm{~K}^{-4}\right) T^{4} $$ Hint: Use Equation $5.110$ to evaluate the integral. Note that $\zeta(4)=\pi^{4} / 90$.
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