Can someone help me with this please?(adsbygoogle = window.adsbygoogle || []).push({});

B(f) = [(2hf^3)/c^2]{1/[exp (hf/kT) - 1]} - Planck law in terms of frequency.

"Derive expressions for B(f) for the cases i. hf << kT, ii. hf >> kT".

I've done the first bit, that's just using a Taylor expansion. The second bit is where I'm stuck. In my lecture notes, I have that for hf >> kT, B(f) = [(2hf^3)/c^2]exp(-hf/kT). What I don't understand is why it's like that. If hf >> kT, shouldn't that exponential tend to infinity?

Thanks.

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Need help with blackbody radiation

**Physics Forums | Science Articles, Homework Help, Discussion**