Optical Phenomena and

Properties of Matter

16

16.1 Introduction ESCHA

For centuries physicistsargued about whether light was a particle or awave. It was

assumed that light couldonly be one or the other, but not both.

In earlier chapters on waves and optics, you studied how light or other electromagnetic

radiation propagates like a wave. The wave nature of light was demonstrated by the

propagation of light inexamples such as diffraction, interference, andpolarisation of

light.

You also saw in Electromagnetic Radiation how light sometimes behavesas a particle.

This chapter looks at evidence supporting the particle model of light. The idea that light

can have both wave andparticle properties was one of the most important discoveries

of the twentieth century.

See introductory video:VPpxi at http://www.everythingscience.co.za

16.2 The transmission and scattering of light

ESCHB

Energy levels of an electron ESCHC

We have seen that theelectrons in an atom have different energy levels. When the

electron receives enough energy, it can jump upto a higher energy level.This is called

’exciting’ the electron. When theelectron in a high energy level sheds some energy, it

drops to a lower energylevel.

We have also seen that the energy associated with light at a specific wavelength is given

by:

E =

hc

λ

.

In the particle model oflight, this means that each packet of light (photon) at a wave-

length λ has energy:

E =

hc

λ

.