This is a lovely demo shown to me by Andreas Tober, the Physics technician at Alleyn’s School in Dulwich, London (which also happens to be the secondary school I attended. I left shortly before Andreas started, but we’ve somehow managed to become friends anyway. Gotta love the internet). I think this is a lovely, simple way to introduce the idea of absorption spectra. I will definitely be using it in my physics teaching next year.
3 thoughts on “Flames and Shadows”
This is a great demo for the minds on Predict-Explain-Observe-Explain approach.
Lovely. Nice clip. I used this experiment to introduce absorption spectra. Isn’t it an old Nuffield demo? I remember taking a group of A level Physics students to visit Aberystwyth University physics department and they went one stage better. They arranged the pole pieces of a strong electromagnet [a large demountable transformer with pole pieces instead of the cross bar] on either side of the flame. The result? No shadow because the magnetic field splits the energy levels [the Zeeman effect].
I also used a white light source [the 12 V, 100 W planar light source which we also used for the Nuffield Young slits demo] and a yellow Bunsen flame. This resulted in a shadow – continuous emission spectrum from the Bunsen flame would also demonstrate a continuous absorption spectrum.
3 Brynceinion, Waunfawr, Aberystwyth SY23 3PN
Its a great demo and even more impressive with a paper towel soaked in saturated NaCl solution. The bunsen flame goes super orange and the shadow is massive.