- #1
Jonsson
- 79
- 0
Hello there,
Plack law of radiation
$$
B(\nu) = \frac{2\,h\,\nu^3}{c^2(e^{h\nu/kT}-1)}
$$
I want to show that for small frequencies, Reyleigh-Jeans law:
$$
B(\nu) = \frac{2\nu^2kT}{c^2}
$$
is correct.
I take the limit of Planck law as ##\nu \to 0## using l'hopital rule:
$$
\lim_{\nu \to 0} \frac{2\,h}{c^2} \frac{\nu^3}{e^{h\nu/kT}-1} \stackrel{\text{l'H}}{=} \lim_{\nu \to 0} \frac{2\,h}{c^2} \frac{3\nu^2kT}{e^{h\nu/kT}h} = 0
$$
I am off by a factor of 3. What is wrong with my maths?
Thank you for your time.
Kind regards,
Marius
Plack law of radiation
$$
B(\nu) = \frac{2\,h\,\nu^3}{c^2(e^{h\nu/kT}-1)}
$$
I want to show that for small frequencies, Reyleigh-Jeans law:
$$
B(\nu) = \frac{2\nu^2kT}{c^2}
$$
is correct.
I take the limit of Planck law as ##\nu \to 0## using l'hopital rule:
$$
\lim_{\nu \to 0} \frac{2\,h}{c^2} \frac{\nu^3}{e^{h\nu/kT}-1} \stackrel{\text{l'H}}{=} \lim_{\nu \to 0} \frac{2\,h}{c^2} \frac{3\nu^2kT}{e^{h\nu/kT}h} = 0
$$
I am off by a factor of 3. What is wrong with my maths?
Thank you for your time.
Kind regards,
Marius