Presentation on theme: "Reflection and Refraction of Light"— Presentation transcript:
1 Reflection and Refraction of Light Chapter 22Reflection and Refractionof LightConceptual questions: 9,11,16,17,18Quick quizzes: 2,3,4Problems: 21,28,49,56
2 Dual Nature of LightExperiments display either the wave nature or the particle nature of lightNature prevents testing both qualities at the same time“Particles” of light are called photonsEach photon has a particular energyE = h ƒh is Planck’s constanth = 6.63 x J s
3 Geometric Optics – Using a Ray Approximation Light travels in a straight-line path in a homogeneous mediumThe ray approximation is used to represent beams of lightA ray of light is an imaginary line drawn along the direction of travel of the light beams
4 Ray ApproximationA wave front is a surface passing through points of a wave that have the same phase and amplitudeThe rays, corresponding to the direction of the wave motion, are perpendicular to the wave fronts
5 Reflection of LightA ray of light, the incident ray, travels in a mediumWhen it encounters a boundary with a second medium, part of the incident ray is reflected back into the first mediumThis means it is directed backward into the first medium
6 Specular ReflectionSpecular reflection is reflection from a smooth surfaceThe reflected rays are parallel to each other
7 Diffuse ReflectionDiffuse reflection is reflection from a rough surfaceThe reflected rays travel in a variety of directionsDiffuse reflection makes the road easy to see at night
8 Law of Reflection The normal is a line perpendicular to the surface The incident ray makes an angle of θ1 with the normalThe reflected ray makes an angle of θ1’ with the normalThe angle of reflection is equal to the angle of incidenceθ1= θ1’
10 Refraction of LightThe incident ray, the reflected ray, the refracted ray, and the normal all lie on the same planeThe angle of refraction, θ2, depends on the properties of the mediumv – speed of light
11 QUICK QUIZ 22.2If beam 1 is the incoming beam in the figure below, which of the other four beams are reflected and which are refracted?
12 Refraction Details v1>v2 The angle of refraction is less than the angle of incidenceThe ray bends toward the normal
13 Refraction Details v1<v2 The angle of refraction is greater than the angle of incidenceThe ray bends away from the normal
14 The Index of Refraction Refraction occurs because the speed of light is different in the two mediaThe index of refraction, n, of a medium can be defined
15 Frequency Between Media As light travels from one medium to another, its frequency does not changeBoth the wave speed and the wavelength do change
16 Index of Refraction Extended f = f1 = f2v1 = ƒ λ1 v2 = ƒ λ2The ratio of the indices of refraction of the two media can be expressed as
17 Snell’s Law of Refraction n1 sin θ1 = n2 sin θ2θ1 is the angle of incidence30.0° in this diagramθ2 is the angle of refraction
20 QUICK QUIZ 22.3A material has an index of refraction that increases continuously from top to bottom. Of the three paths shown in the figure below, which path will a light ray follow as it passes through the material?
21 QUICK QUIZ 22.4As light travels from vacuum (n = 1) to a medium such as glass (n > 1), which of the following properties remains the same: (a) wavelength, (b) wave speed, or (c) frequency?
22 Problem 22.21The light shown in the figure makes an angle of 20o with the normal NN’ in the linseed oil (n=1.48). Determine angles q and q’.
23 Problem 22.28A cylindrical cistern, constructed below ground level, is 3.0 m in diameter and 2.0 m deep and is filled to the brim with a liquid whose index of refraction is 1.5. A small object rests on the bottom of the cistern at its center. How far from the edge of the cistern can a girl whose eyes are 1.2 m from the ground stand and still see the object?
24 DispersionThe dependence of the index of refraction on λ is called dispersion
25 Refraction in a Prism δ the angle of deviation n(l) Since all the colors have different angles of deviation, they will spread out into a spectrumViolet deviates the mostRed deviates the least
26 Using Spectra to Identify Gases All hot, low pressure gases emit their own characteristic spectraThe particular wavelengths emitted by a gas serve as “fingerprints” of that gasSome uses of spectral analysisIdentification of moleculesIdentification of elements in distant starsIdentification of minerals
27 The Rainbow At the back surface the light is reflected It is refracted again as it returns to the front surface and moves into the airThe rays leave the drop at various anglesThe angle between the white light and the violet ray is 40°The angle between the white light and the red ray is 42°
30 Huygen’s PrincipleHuygen assumed that light is a form of wave motion rather than a stream of particlesAll points on a wave front produce spherical secondary waves, which propagate in the forward direction with speeds characteristic of waves in that medium
31 Huygen’s Principle and the Law of Refraction In time Δt, ray 1 moves from A to B and ray 2 moves from A’ to CFrom triangles AA’C and ACB, all the ratios in the Law of Refraction can be foundn1 sin θ1 = n2 sin θ2
32 Total Internal Reflection Total internal reflection can occur when light attempts to move from a medium with a high index of refraction to one with a lower index of refractionRay 5 shows internal reflection
33 Critical AngleThe critical angle is an angle of incidence that will result in an angle of refraction of 90°
35 Conceptual questions18. If a beam of light with a given cross-section enter a new medium, the cross section of the refracted beam isa) largerb) smallerc) not changed9. In dispersive materials, the angle of refraction for a light ray depends on the wavelength of light. Does the angle of reflection depend on the wavelength?11. Explain why a diamond loses most of its sparkle when submerged in carbon disulfide.16. Explain why an oar partially in water appears to be bent.17. Why do astronomers looking at distant galaxies talk about looking backward in time?
36 Problem 22.56A laser beam strikes one end of a slab of material, as in Figure P The index of refraction of the slab is Determine the number of internal reflections of the beam before it emerges from the opposite end of the slab.
38 Problem 21-49As shown in Figure P22.49, a light ray is incident normally on one face of a 30°-60°-90° block of dense flint glass (a prism) that is immersed in water. (a) Determine the exit angle θ4 of the ray. (b) A substance is dissolved in the water to increase the index of refraction. At what value of n2 does total internal reflection cease at point P?
39 Review questions1. Visible light of which color bends the most when changing mediums?A. yellowB. greenC. violetD. red
40 2. Water has an index of refraction of 1. 3 2. Water has an index of refraction of Approximately how fast does light move through the water?1.0 x 108 m/s b x 108 m/s3.0 x 108 m/s d x 108 m/s3. The sky is blue because itAbsorbs light at 390 nmReflects light at 390 nmAbsorbs light at 700 nmReflects light at 700 nm