pse4 lecture ch32
TRANSCRIPT
11/18/09
Lecture PowerPoint Chapter 32 Physics for Scientists and Engineers, with Modern Physics, 4th edition Giancoli 2009 Pearson Education, Inc. This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials.
Chapter 32 Light: Reflection and Refraction
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Units of Chapter 32 The Ray Model of Light y g Reflection; Image Formation by a Plane Mirror Formation of Images by Spherical Mirrors Index of Refraction Refraction: Snells Law
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Units of Chapter 32 Visible Spectrum and Dispersion ; p Total Internal Reflection; Fiber Optics Refraction at a Spherical Surface
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32-1 The Ray Model of LightLight very often travels in straight lines. We represent light using rays, which are straight lines emanating from an object This is an object. idealization, but is very useful for geometric optics.
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32-2 Reflection; Image Formation by a Plane MirrorLaw of reflection: the angle of reflection (that the (th t th ray makes with the normal to a k ith th lt surface) equals the angle of incidence.
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32-2 Reflection; Image Formation by a Plane MirrorWhen light reflects from a rough surface, the law of reflection still holds but the angle of holds, incidence varies. This is called diffuse reflection.
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32-2 Reflection; Image Formation by a Plane MirrorWith diffuse reflection, your eye sees reflected light at all angles. With specular reflection (from a mirror), mirror) your eye must be in the correct position.
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32-2 Reflection; Image Formation by a Plane MirrorExample 32-1: Reflection from flat mirrors. Two flat mirrors are perpendicular to each other. An incoming beam of light makes an angle of 15 with the first mirror as shown. What angle will the outgoing beam make with the second mirror?
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32-4 Index of RefractionIn general, light slows somewhat when traveling through a medium. medium The index of refraction of the medium is the ratio of the speed of light in vacuum to the speed of light in the medium: g
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32-5 Refraction: Snells LawLight changes direction when crossing a boundary from one medium to another. This is called refraction, and the angle the outgoing ray makes with the normal is called the angle of refraction.
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32-5 Refraction: Snells LawThe angle of refraction depends on the indices of refraction, and is given by Snells law: S
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32-5 Refraction: Snells LawExample 32-8: Refraction through flat glass. Light traveling in air strikes a flat piece of uniformly thick glass at an incident angle of 60, as shown. If the index of refraction of the glass is 1.50, (a) what is the angle of refraction A in the glass; (b) what is the angle B at which the ray emerges from the glass?Copyright 2009 Pearson Education, Inc.
32-5 Refraction: Snells LawExample 32-9: Apparent depth of a pool. A swimmer has dropped her goggles to the bottom of a pool at the shallow end, marked end as 1.0 m deep. But the goggles dont look that deep. Why? How deep do the goggles appear to be when you look straight down into the water?
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Example 32-9: Apparent depth of a pool.Copyright 2009 Pearson Education, Inc.
32-6 Visible Spectrum and DispersionThe visible spectrum contains the full range of wavelengths of light that are visible to the human eye. eye
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32-6 Visible Spectrum and DispersionThe index of refraction of many transparent materials, such as glass and water, varies slightly with wavelength. This is how prisms and water droplets create rainbows from sunlight.
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32-6 Visible Spectrum and DispersionThis spreading of light into the full spectrum is called dispersion.
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32-6 Visible Spectrum and DispersionConceptual Example 32-10: Observed color of light under water. We said that color depends on wavelength. For example, for an object emitting 650 nm light in air, we see red. But this is true only in air. If we observe this same object when under water, it still looks red. But the wavelength in water n is 650 nm/1.33 = 489 nm. Light with wavelength 489 nm would appear blue in air. Can you explain why the light appears red rather than blue when observed under water?Copyright 2009 Pearson Education, Inc.
http://www.siteprocentral.com/html_color_code.htmlCopyright 2009 Pearson Education, Inc.
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Blue: Y2SiO4:Ce3+ Green: Zn2SiO4:Mn2+ Y2O3:Eu3+Copyright 2009 Pearson Education, Inc.
The electromagnetic spectrum and the classification of regions
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Light can only be absorbed or emitted in discrete quanta, known as photons, each of which possess a definite amount of energy described by Planck's equation.
Where: h = Planck's constant (6.6256 x 10-34 J s photon-1), c = speed of light (2.9979 x 108 m s-1), = wavelength of radiation (m), n = frequency of radiation (s-1), = corresponding wave number (m-1).
1239 h hc = = e ( nm ) e E ( eV ) 4 Wave ~ particle duality 10 = 1 ( cm 1 ) = 1 . 239 E ( eV ) =Copyright 2009 Pearson Education, Inc.
32-7 Total Internal Reflection; Fiber OpticsIf light passes into a medium with a smaller index of refraction, the angle of refraction is larger. There is an angle of incidence for which the angle of refraction will be 90; this is called the critical angle:
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32-7 Total Internal Reflection; Fiber OpticsIf the angle of incidence is larger than this, no transmission occurs. This is called total internal reflection. f
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32-7 Total Internal Reflection; Fiber OpticsOptical fibers also depend on total internal reflection; they are therefore able to transmit light signals with very small losses.
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The Nobel Prize in Physics 2009
Charles K. Kao
Willard S. Boyle
George E. Smith
for groundbreaking achievements concerning the transmission of light in fibers for optical communicationCopyright 2009 Pearson Education, Inc.
for the invention of an imaging semiconductor circuit th CCD i d t i it the sensor
Summary of Chapter 32 Light paths are called rays. Index of refraction: Angle of reflection equals angle of incidence. Plane mirror: image is virtual, upright, and the same size as the object. Spherical mirror can be concave or convex. convex Focal length of the mirror:
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Summary of Chapter 32 Mirror equation:
Magnification:
Real image: light passes through it. Virtual image: light does not pass through.
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Summary of Chapter 32 Law of refraction (Snells law):
Total internal reflection occurs when angle of incidence is greater than critical angle:
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