Light Waves Chapter 29 Light travels like a

Light Waves Chapter 29 Light travels like a wave and hits like a particle.

Fig. 29. 1 Crests are called wave fronts.

Huygen’s Principle Wave fronts made up of tinier wave fronts.

Spherical Wave Fronts Point along wave front AA’ are sources of new wavelets Overlapping wavelets will form a new surface BB’

Fig. 29. 3 Animation

Meter stick makes “plane waves” Plane waves – straight line waves like sheets. Sun produces “plane waves” Water diffracts (bends) through the opening.

Wave Diffraction – type of light bending. Works for other types of waves. Diffraction of “plane” water waves. True for light waves.

A) Opening larger than wavelength of the incident light (sharp shadow) abrupt changes from light to dark. B) Narrow opening. Light diffracts. Fuzzy shadow (edges). Gradual changes from light to dark.

Fig. 29. 8 Animation Diffraction depends on the wavelength of the wave compared to the size of the objet that casts the shadow.

Interference Crests overlap crests or crests overlap troughs.

Wave Interference Constructive and destructive interference.

Interference is a property of all waves Interference patterns of overlapping waves from two vibrating sources.

1801 Thomas Young Famous Double Slit Interference Experiment Demonstrates the wave nature of light. Pattern of light and dark fringes.

Double Slit Experiment Fringe patterns with two closely spaced thin slits.

Fig. 29. 18 Animation

Double slit experiment with a laser (photons) borrowed from Ch. 31

Bright area – waves from both slits arrive in phase (constructive) Dark area – overlapping of waves that are out of phase (destructive)

Fringe Patterns

Fig. 29. 19 Animation

Single Slit Pattern Simple diffraction pattern

Interference Pattern Graphical representation

Interference does not create or destroy light energy but redistribute it. You can use more than two slits to get “diffraction grating”. ◦ Separates colors by interference ◦ Prisms use refraction – other type of bending.

Demos

Videos http: //www. youtube. com/watch? v=w. Ez. Rd. ZG YNv. A http: //www. youtube. com/watch? v=UANVMIaj ql. A http: //www. youtube. com/watch? v=oxknfn 97 v. FE

Chapter 29 Homework Review Questions: 1 -7 ◦ Number 5 read to find answer Exercises: 1, 2, 3, 5, 10, 11, 12, 14, 16, 17, 21, 23 ◦ 11 and 12 are harder questions We only covered part of the chapter, for the exam, read pages 558 -566 Extra Credit: Project 1

Chapter 31 More similar interesting stuff in Chapter 31: Light quanta Read pg. 600, 605 -610 Interference patterns for photons (particles of light) and electrons!

Figure 31. 5

Stages of Photon interference pattern

Diffraction fringes of a) light and b) electron beam

Figure 31. 11