Download Wave Nature of Light

So far, we’ve studied some elements of the nature of
light: reflection, refraction
Isaac Newton
 In his day, Newton was most famous for his work on
light.
 He described light as a beam of ultra-tiny particles.
 This could explain reflection and refraction, but
couldn’t explain others.
 In the following centuries, light began to be thought of
as a WAVE.
Huygen’s Principle
 Christian Huygens – Dutch mathematician/scientist
 Described light waves spreading out from a point
source as the overlapping of tiny secondary wavelets.
Saw this with Ripple Tank
 Wide opening in barrier
 Wave goes right through,
Bending around corners
 With narrow opening,
More pronounced bending
On Ripple Tank, we saw Diffraction
and Interference
 Diffraction – bending of wave by anything other than
reflection or refraction
 Interference – overlapping of waves, producing areas
of constructive and destructive interference.
Interference Patterns
 We saw that increasing the frequency  longer
wavelength, wider pattern
 We saw that bringing sources together  wider also
Do we see these things with light?
 Diffraction – laser on razor blade edge
 Light bends around edges
Send light through tiny slit
 Do we see interference pattern?
 What happens if we narrow the slit width?
Patterns
 Different wavelengths of
light produce different
patterns.
 Longer wavelengths,
wider pattern.
 (So red wider pattern
than green)
White Light Separates
 Send white light through diffraction grating, get
separation of colors according to wavelength.
Compact Discs/DVDs
 The tracks of a CD or DVD act as a diffraction grating,
producing a separation of the colors of white light.
 Opals, too!
Doppler Effect with Light
 Like with sound waves, if a
light source is moving
towards an observer, they
would experience a higher
frequency (shift to blue end
of spectrum)
 Likewise, a light source
moving AWAY would be
shifted to red end of
spectrum.
Red Shift of Stars
 The fact that light from ALL
distant stars and galaxies is
red-shifted is convincing
evidence that the universe is
expanding.
Evidence that Light is a WAVE
 Light shows diffraction
 Light shows interference patterns
 Light shows Doppler effect
 Huygens, Young experiments
 Maxwell’s Theory (electromagnetic wave theory)