# Homework Help: Planck's Formula - Help undressing the question needed!

1. Apr 29, 2006

### Brewer

I have a question that asks me to plot Plancks forumla for the wavelength dpendence of the intensity of black body radiation, and to use it to obtain an estimate for the temperature at which an object glows red hot.

Now I know Planck's formula (or its written in front of me), but I don't know what band of wavelengths I should plot. The EM spectrum? Other random wavelengths?

And for the red hot bit, is that the point at which the peak of the plot goes over a certain wavelength? The infra red end of the spectra?

Any help would be appreciated.

2. Apr 29, 2006

### lightgrav

Plot the portions of the spectrum that contain noticeable intensity ...
for a Temperature at which there's noticeable intensity in the "red".

The question author probably expects you to use a Temperature at which
the PEAK of the distribution is red (for whatever variable your equation is in)
- but this would appear orange-hot, with significant orange and yellow -
I would rather set the peak at the infra-red edge of visible ...
even better, set the high-f inflection point at the infrared edge of visible.

[just because HUMANS can't see it , doesn't mean it isn't worth graphing!]

3. May 1, 2006

### Brewer

So it is the point at which the peak of the graph is in the infra-red part of the spectrum then?