Demonstration of Dispersion of White Light Apparatus White light source, ray box, prism (or diffraction grating), white screen
Procedure Shine the narrow beam of white light through the prism (or diffraction grating) onto a white screen.
Observation
All the colours of the spectrum are visible on the screen. Conclusion
White light is made up of all the colours (wavelengths) of visible light.
Glass prism Fig 14.19 Screen Red
Orange Yellow Green Blue Indigo Violet
Recombination
A second prism will recombine the constituents of white light to again form white light. Refraction is the cause of both the dispersion and the recombination, (Fig 14.20).
SCIENCE,TECHNOLOGY & SOCIETY
Colours seen on surfaces of compact discs A CD is composed of clear plastic, which has microscopic bumps impressed on it. A thin, reflective aluminium layer covers the bumps. Fig 14.21 shows a cross-section of a CD and a magnified diagram of the aluminium. CDs are read by reflecting a laser off this surface.
Aluminium Acrylic Label
125 mm 1.2 mm Polycarbonate plastic
Fig 14.20: Recombination of dispersed light back to white light
0.5 microns 1.6 microns 0.5 microns Fig 14.21: Diagrams illustrating the bumps on a CD
