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WyzZero
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First time here, and looking for help on this. The 2nd part of this problem, I have seen some posts on and am still reviewing, but haven't found much on the 1st part.
1) Use l'Hopital's Rule to show that
$${\lim_{\lambda\rightarrow 0^{+}}=0}\text{ and }\lim_{\lambda\rightarrow \infty}=0$$
for Planck's Law. So this law models blackbody radiation better than the Rayleigh-Jeans Law for short wavelengths.
2) Use a Taylor polynomial to show that, for large wavelengths, Planck's Law give approximately the same values as the Rayleigh-Jeans Law.
Rayleigh-Jeans Law expresses the energy density of blackbody radiation of wavelength ##\lambda## as
$$f(\lambda) =\frac{8{\pi}kT}{{\lambda}^{4}}$$
In 1900 Max Planck found a better model (known now as Planck's Law) for blackbody radiation:
$$f(\lambda) =\frac{8{\pi}hc{\lambda}^{-5}}{e^{\frac{hc}{{\lambda}kT}}-1}$$
where ##\lambda## is measured in meters, T is the temperature (in kelvins), and
##h## = Planck's constant ##= 6.6262 * 10^{-34} J*s##
##c =## speed of light ##= 2.997925 * 10^{8} m/s##
##k =## Boltzmann's constant ##= 1.3807 * 10^{-23} J/K##
For part one, I used L'Hopital's Rule on
$$f(\lambda) =\frac{8{\pi}hc{\lambda}^{-5}}{e^{\frac{hc}{{\lambda}kT}}-1}$$
and got
$$\frac{40{\pi}kt{\lambda}^{-4}}{e^{\frac{hc}{{\lambda}kT}}}$$
Finding this, I decided to do this a few times, slowly removing the ##\lambda^{-x}## until I got:
$$\frac{960{\pi}k^{5}T^{5}}{h^{4}c^{4}e^{\frac{hc}{{\lambda}kT}}}$$
Using $${\lim_{\lambda\rightarrow 0^{+}}} \frac{960{\pi}k^{5}T^{5}}{h^{4}c^{4}e^{\frac{hc}{{\lambda}kT}}}$$ I compare this to ##\lim_{\lambda \rightarrow 0^{+}} \frac{1}{e^{\frac{1}{\lambda}}}## and ##e^{\frac{1}{\lambda}}## decreases to 0 so this goes to 0, but how do I show the same, as the limit of ##\lambda## goes to ##\infty##?
AM I doing something wrong?Also, I am looking at one of the old posts for part 2 (I found on this board), but if you have anything to add to it here, it would be much appreciated.
Thanks in advance for any help you can provide.
Homework Statement
1) Use l'Hopital's Rule to show that
$${\lim_{\lambda\rightarrow 0^{+}}=0}\text{ and }\lim_{\lambda\rightarrow \infty}=0$$
for Planck's Law. So this law models blackbody radiation better than the Rayleigh-Jeans Law for short wavelengths.
2) Use a Taylor polynomial to show that, for large wavelengths, Planck's Law give approximately the same values as the Rayleigh-Jeans Law.
Homework Equations
Rayleigh-Jeans Law expresses the energy density of blackbody radiation of wavelength ##\lambda## as
$$f(\lambda) =\frac{8{\pi}kT}{{\lambda}^{4}}$$
In 1900 Max Planck found a better model (known now as Planck's Law) for blackbody radiation:
$$f(\lambda) =\frac{8{\pi}hc{\lambda}^{-5}}{e^{\frac{hc}{{\lambda}kT}}-1}$$
where ##\lambda## is measured in meters, T is the temperature (in kelvins), and
##h## = Planck's constant ##= 6.6262 * 10^{-34} J*s##
##c =## speed of light ##= 2.997925 * 10^{8} m/s##
##k =## Boltzmann's constant ##= 1.3807 * 10^{-23} J/K##
The Attempt at a Solution
For part one, I used L'Hopital's Rule on
$$f(\lambda) =\frac{8{\pi}hc{\lambda}^{-5}}{e^{\frac{hc}{{\lambda}kT}}-1}$$
and got
$$\frac{40{\pi}kt{\lambda}^{-4}}{e^{\frac{hc}{{\lambda}kT}}}$$
Finding this, I decided to do this a few times, slowly removing the ##\lambda^{-x}## until I got:
$$\frac{960{\pi}k^{5}T^{5}}{h^{4}c^{4}e^{\frac{hc}{{\lambda}kT}}}$$
Using $${\lim_{\lambda\rightarrow 0^{+}}} \frac{960{\pi}k^{5}T^{5}}{h^{4}c^{4}e^{\frac{hc}{{\lambda}kT}}}$$ I compare this to ##\lim_{\lambda \rightarrow 0^{+}} \frac{1}{e^{\frac{1}{\lambda}}}## and ##e^{\frac{1}{\lambda}}## decreases to 0 so this goes to 0, but how do I show the same, as the limit of ##\lambda## goes to ##\infty##?
AM I doing something wrong?Also, I am looking at one of the old posts for part 2 (I found on this board), but if you have anything to add to it here, it would be much appreciated.
Thanks in advance for any help you can provide.
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