Week 8 Lecture notes with Ch. 17 Book notes
Week 8 Lecture notes with Ch. 17 Book notes PHYS 202
Popular in General Physics >4
verified elite notetaker
Popular in Physics 2
This 4 page Class Notes was uploaded by Melissa on Sunday February 28, 2016. The Class Notes belongs to PHYS 202 at University of Oregon taught by Jenkins T in Fall 2015. Since its upload, it has received 19 views. For similar materials see General Physics >4 in Physics 2 at University of Oregon.
Reviews for Week 8 Lecture notes with Ch. 17 Book notes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 02/28/16
• 17.1 what is light 3 models ‣ Wave model-light travels in wave like patterns • Known as wave optics ‣ Ray model • Light travels in a straight line ‣ Photon model • Light consists of photons that have both wavelike and particle like properties The propagation of light waves ‣ Spreading of waves is called diﬀraction • Waves spread out from the opening rather than continuing in a straight line ‣ Wavelength of light is short ‣ How far a light wave spreads out depends on the size of the objects with which the wave interact ‣ Light has a dual nature • sometimes it looks like a wave while other times it looks like it acts like a particle • Principle of complementarity: wave and particle aspects of light are fundamental to its nature Light is an electromagnetic wave ‣ due to the rapid oscillations and magnetic ﬁelds ‣ Do not require a material medium to travel • because of this they are NOT mechanical waves ‣ Travel in a vacuum at the speed of light ‣ Prisms spread out the diﬀerent wavelengths of light which in turn results in WHITE light because the colors or wavelengths have combined • The colors that are seen are considered part of the visible spectrum ‣ Particles of light are called photons ‣ Can have any wavelength Index of Refraction ‣ Light tends to slow down as it passes through transparent materials such as glass and water ‣ Speed of light of a material is characterized by the index of refraction or N • • Index of refraction are higher for for liquids and solids because they have higher density of atoms for light to interact with ‣ Depends slightly on wavelength • wavelength in a transparent material is shorter than the wavelength in a vacuum • ‣ Frequency remains the same as it moves from one medium to another • 17.2 The interference of light Young.'s Double-Slit experiment • due to the narrow slits, light spreads out behind each slit and the two spreading waves overlap in the region between the slits and the screen • There will be interference • Like sound waves there will be constructive and destructive interference Constructive when the intensity of the light is high and the distances between R1 and R2 diﬀered by a whole number of wavelengths ‣ ‣ Destructive when the distances diﬀer by a whole number plus half of a wavelength: will appear dark!! Brightest point will be at m=0 and is called the central maximum ‣ Interference pattern is a series of equally spaced bright lines ‣ • 17.3 The Diﬀraction Grating Consists of a large number of equally spaced narrow slits or lines Light intensity pattern on a screen behind a diﬀraction grating is due to the interference of N overlapped waves A transmission grating has slits while a reﬂection grating has lines that reﬂect light If a plane wave of a wavelength approaches from the left and the crest of the wave arrives simultaneously at each of the slits, causing the wave emerging from each slit to be in phase with wave emerging from every other slit Path followed by the light from one slit to a point on the screen is nearly parallel to the path followed by light from the other slits N light waves, from N diﬀerent slits, will all be in phase with each other when they arrive at a point on a screen at the angle ‣ In comparing multiple slit diﬀraction to two slit diﬀraction, the multiple slit has bright fringes that are much narrower ‣ As the number of slits increases, the bright fringes get narrower but brighter • 17.4 Thin-ﬁlm Interference Equal frequency light waves are produced when partial reﬂection at a boundary splits a light wave into a reﬂected wave and a transmitted wave Light will reﬂect from both the bottom and the top of the layer, causing interference ‣ Soap bubbles and oil slicks Interference of Reﬂected Light Waves ‣ a light wave is partially reﬂected from any boundary between two transparent media with diﬀerent indices of refraction ‣ If light moves from a medium with a higher light speed or lower index of refraction to a medium with a higher index of refraction, the reﬂected wave will be inverted • inverted wave is known as the phase change undergoes a phase change if it reﬂects from a boundary at which the index of refraction increases • Physical path diﬀerence is about twice the thickness of the ﬁlm • Wavelength of the light will be diﬀerent in the ﬁlm than in a vacuum or air and the reﬂection may or may not involve phase changes • If neither or both waves have a phase change due to reﬂection, the net addition to the path length diﬀerence is zero so the eﬀective path-length diﬀerence is. • If only one wave has a phase change due to reﬂection, the eﬀective path length diﬀerence is increased by one half wavelength to The Colors of Soap Bubbles and Oil Slicks ‣ light waves reﬂect from both surfaces of the ﬁlm and the reﬂected waves interfere • light reﬂecting from front has a reﬂective phase change but the back reﬂection does not • 17.5 Single-Slit Diﬀraction Diﬀraction is the bending of wave as it passes through an opening or around an obstacle Amount of diﬀraction depends on the ration of the wavelength to the size of the opening of the object Single-slit diﬀraction ‣ diﬀraction through a tall, narrow, slit of width a ‣ Light from one part of the slit interferes with the light from another part of the slit ‣ If screen is far from the slit, the Rays through it are parallel • far-ﬁeld diﬀraction ‣ Central fringe is bright because all the Rays follow essentially the same path, arrive at the screen in phase, and interfere constructively ‣ First minimum: occurs where waves from bottom half of slit travel a half of wavelength farther than waves from the top half • ‣ 2nd: where part of of the light arrives a t screen out of phase and rest of the light arrives in phase; dimmer than central maximum • 17.6 Circular- Aperture Diﬀraction light waves passing through a circular aperture spread out to produce a circular diﬀraction pattern ‣ minimum located at ‣ Diﬀraction limits the resolution of optical instruments