Topic Summary
Interference and Diffraction in a Nutshell.
(it may be helpful to review concepts on waves in Chapter 11 before beginning)
(it may be helpful to review concepts on waves in Chapter 11 before beginning)
_Double-Slit Interference:
A wave-interference phenomenon occurs
when light passing through one slit interferes with light passing
through another slit. The result is a pattern on a screen
placed a distance away from the slit.
d : distance between the slits
Ө : angle between rays from each slit (approximately parallel) and the horizontal
Ө : angle between rays from each slit (approximately parallel) and the horizontal
y: distance from fringe to center of diffraction pattern
L: distance from slits to screen
Ө: angle between rays from each slit and the horizontal
L: distance from slits to screen
Ө: angle between rays from each slit and the horizontal
Single-Slit Diffraction
A diffraction pattern exists around any sharp object illuminated by a point source. Light diffracts after encountering an obstacle; a detailed reason can be seen in the Extras section under Huygens' Principle.
D: width of a single slit
Ө: angle between light rays and horizontal
Ө: angle between light rays and horizontal
Diffraction Grating
A large number of equally spaced parallel slits through which light can travel. Once again, a pattern is formed on a screen due to diffraction.
Thin Film Interference
A picture is worth a thousand words.
Light that travels through the film before being reflected must travel a long path than light that is directly reflected by medium 1. A viewer sees a bright surface when the waves arrive in phase (constructive interference) while seeing a dark surface when the waves arrive completely out of phase (destructive interference). Sometimes, the waves change phase by 1/2 cycle upon reflection.
Waves undergo phase changes when reflected by a material with a refraction index greater than that of the material in which it is traveling.
Eg: Light travels through air (n=1) and is reflected by water (n=1.33)
Eg: Light travels through air (n=1) and is reflected by water (n=1.33)
Even number of phase changes:
Odd number of phase changes:
Polarization
A wave is said to be polarized or plane-polarized if its oscillations are limited to a single plane. Light originally travels in all directions, but it can be limited to only oscillate in a single plane.
Light is polarized when it travels through a polarizer. Its intensity is also reduced by the polarizer.
Light can also be polarized by reflection, when light strikes a nonmetallic surface at any angle other than the perpendicular.
Chapter done by Justin Tzeng.