Re: Why does the spectrum change when viewed through a water prism?

Jill

I suspect the basic reason is that black paper, being dyed, absorbs most of the 
lower visible light frequencies. Black colouration is achieved by adding a 
number of chemical dyes into the paper. Each chemical will absorb light at 
different frequencies. The black paper is also an imperfect black body, so it 
will preferentially absorb/emit light in certain frequency range. Hence the 
lower spectrum is absorbed totally leaving only the higher frequencies, blue-
violet and UV. 


White paper, not being dyed, simply reflects the visible light back off itself. 
This may be complicated by paper manufacturers bleaching the paper. The bleaches 
used will absorb some light, as will the paper. Paper after all is not a mirror. 


As a test of my reasoning try different black papers and other colours to view 
the spectrum on. What happens if you use red, green or yellow paper to display 
the spectrum on. This is a good way to show how filters work and get the 
students thinking about why emission/absorbtion works. 


Yours

Dave Barlow