This photo was taken using a diffraction grating and a bright lamp. Diffraction occurs when a wave spreads out and changes direction after passing through an opening or around a barrier. Light behaves like a wave, as demonstrated in the double slit experiment: when monochromatic light shines through two narrow slits, a pattern of alternating bright and dark bands forms as light diffracts through the slits, and the 2 resultant waves interfere. Bright bands result from constructive interference (when two crests and a through cancel each other out).
A diffraction consists of many small slits or holes through which light diffracts. From the equation dsin(0)=nλ (d=distance between adjacent slits, λ=wavelength, 0=angle between a resultant ray and the normal to the grating) light of different wavelengths (colours) diffract at different angles. This is why white, continuous-spectrum light separates into a “rainbow”. Because red light has longer wavelength than green and blue, its 0 is greater and it diffracts farther away from the normal and the centre of the photo. The bright spots are points of constructive interference, and the dark spots, destructive.
These pictures are included in the Art of Physics travelling exposition. To get more information on how your institution can host the travelling exposition, please contact Francine Ford, CAP's Executive Director at cap@uottawa.ca.
Questions or comments?
