Light: Waves and Particles

 Light is made of waves you do not normally notice, but these waves can be detected and measured under certain circumstances  Like water waves, light waves can be characterized by wavelength (λ) and frequency (ν) Light

 If white light passes through a narrow slit and hits a prism, a rainbow of colours, or continuous spectrum is produced. The light passes through the prism and is refracted or bent  Different frequencies that compose white light bend at different angles causing light wave to separate into colours

Parts of a Wave

 Origin = base line of the energy  Crest= high point on the wave  Trough= low point on a wave  Amplitude = distance from origin to crest  Wavelength = distance from crest to crest  Wavelength is abbreviated λ (Greek letter lambda)

 Are inversely related (as one goes up one goes down)  Units from frequency is cycles/sec or hertz (Hz)  Letter c represents the speed of light = 3.00 x 10 8 m/s  Wavelength is measured in meters (m)  Formula = c = λ ν Frequency and Wavelength

 Ex. Wavelength of blue light is 4.7 x 10-7m What is the frequency?  What is the wavelength (λ) of red light? Ν = 4.3 x s -1 Examples

 light is said to have a duel nature. It can behave like particles or waves or a combination of the two.  During an experiment with hot, glowing substances, Max Planck proposed a relationship between energy of atoms in the solid and the wavelength of light being emitted. Light: Max Planck

 Soon after Albert Einstein expanded Planck’s work by dealing specifically with light energy. Einstein suggested that light was emitted in “packets” of energy and that light was proportional to the frequency of a light wave.  “packets” became known as photons Light: Albert Einstein

 Formula=E = h v  E is the energy of the photon  h is planck’s constanth = x Joules x sec  Joule is the metric unit of energy Energy of a Photon Energy and Frequency E h v

 Ex. If yellow light has a frequency of 5.2 x Hz How much energy does the light have? Example