Physics 106 Lesson #27 Dr. Andrew Tomasch 2405 Randall Lab
[email protected] Interference and Diffraction: The Wave Nature of
Light Slide 2 What Do We Know About Light? EM wave Mostly travels
in straight lines (Ray Tracing) In vacuum light travels at Reflects
with i = r Refracts when passing between media with different index
of refraction: Bends toward the normal when passing into higher n
Snells Law Slide 3 How do We Know Light is a Wave? Distinguishing
features of waves: Interference: two waves can add together and
cancel Diffraction: waves can travel around corners Slide 4
Interference: Thin Films Light waves traveling from one medium to
another undergo partial reflection and partial transmission at the
interface of the two mediums Slide 5 Soap Films Slide 6 Diffraction
Diffraction: The bending of waves around small obstacles and the
spreading of waves beyond small openings Small is defined in
comparison to the wavelength The fact that we can hear sounds
around corners and behind barriers involves both the diffraction
and the reflection of sound waves Slide 7 Huygens Principle Every
point on a wave front acts as a source of tiny wavelets that move
forward with the same speed as the wave The wave front at a latter
instant is the surface that is tangent to the wavelets Slide 8
Diffraction Waves passing through narrow single opening bend and
spread out. The diffraction of light is only noticeable when the
size of the opening is small compared to the wavelength of the
light The amount of bending increases as the size of the opening
decreases Slide 9 Diffraction of a Water Wave The extent of the
diffraction increases as the size of the opening decreases. Slide
10 Single-Slit Diffraction This top view shows five sources of
Huygens wavelets Demonstration Slide 11 The Diffraction Grating We
can replace the sine of the diffraction angle by the ratio of two
sides of a triangle The slits of the grating are perpendicular to
the plane of the page. Slide 12 X-ray Diffraction Complex
diffraction patterns reveal the internal arrangements of crystals
Lower right panel shows the DNA diffraction pattern that lead to
the discovery of the double-helix structure
