# 3/8/6 Propagation of Light Refraction, Polarization, Scattering & Resolution Thursday  Group Project #1 (bring Group Project #1)  Practice Exercises.

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3/8/6 Propagation of Light Refraction, Polarization, Scattering & Resolution Thursday  Group Project #1 (bring Group Project #1)  Practice Exercises (bring PX-1 and PX-2) Friday  Waves and Particles Coming up after Spring Break  Exam #2

Law of Reflection: “Angle of Incidence = Angle of Reflection” Law of Refraction “Snell’s Law”:

ConcepTest #44: A beam of light is incident on the interface between plastic (n = 1.3) and air with a 40 o angle as shown. What is the angle of the refracted ray? 1. 27 o 4. 50 o 2. 31 o 5. 85 o 3. 40 o 6. 90 o (back of card) Not enough info 40 o plastic air

ConcepTest #45: Consider the plastic/air interface from before with n plastic = 1.3. A beam of light is incident on the interface from the plastic side. At a particular angle of incidence for the incoming beam, the refracted ray will disappear. Which of the following is correct for  1 ’ (the angle of the reflected beam) when this occurs? 1. 0 o <  1 ’ < 15 o 4. 45 o <  1 ’ < 60 o 2. 15 o <  1 ’ < 30 o 5. 60 o <  1 ’ < 75 o 3. 30 o <  1 ’ < 45 o 6. 75 o <  1 ’ < 90 o (back of card) This can’t happen

Application: Total Internal Reflection and Fiber Optics Galaxy Wands!

Application: LensesSpooky Spoons

Related Questions: Where does the “Law of Reflection” come from? Why does light change speed in different media? Why does the frequency of light remain constant in different media? Has to do with the ElectroMagnetic nature of light and the interaction of electromagnetic radiation with matter  The Electric field interaction with electrons ElectroMagnetic Radiation Review Changing E  Changing B  Changing E  Changing B, … How to get these kinds of changing fields?  Accelerated charges Polarized vs. Unpolarized Radiation Simulation

ConcepTest #46: A positive charge is undergoing simple harmonic motion in the horizontal direction in the plane of the page. Consider a model polarizer consisting of long thin parallel wires as shown. You hold the polarizer between your eye and the oscillating charge. How should you hold the polarizer so that the electrons in the wires will undergo the most motion?

ConcepTest #47: Consider polarizing filters with their transmission axis indicated by the double arrow. Unpolarized light is sent through the first (back) filter. Given the choices on the right: 1. None of the light 2. Some of the light 3. All of the light 4. Not enough info Consider the filter arrangements shown. How much of the light that makes it through the first filter passes through the last filter? (a) (b) (c)

Polarizing by Absorption & Polarizing Filters Unpolarized light (intensity I ) passes through a single filter: Two filters oriented with transmission axes  =  1 –  2 ; fraction of light that passes through first filter which makes it through second filter: More than two filters? Consider neighboring pairs: Re-Radiation and Polarization  Absorption (lab, toy kit)  Reflection (lab, video demo)  Scattering (lab, video demo)

Re-Radiation and Interference/Diffraction  Reflection  Changing Speeds & Refraction  Scattering Not all wavelengths are equal…  Consider single slit diffraction Scattering: longer wavelengths diffract  bend around corners  get around obstacles more than shorter wavelengths Different wavelengths interfere diffract refract scatter Differently  “dispersion”  rainbows!

ConcepTest #48: A tank contains a water/creamer mixture. White light shines through the tank of water from the bottom. Consider the following choices: a)What is the color of the light that emerges through the top of the tank? b) What is the color of the light that emerges from the side of the tank? 1. Reddish 2. Blueish 3. White 4. Black/no color Think about This: What common childhood question can you now answer?

Application: Scattering and Why the Sky is Blue and Sunsets are Red Scattering and Resolution: Lasers and CDs and Bumps, Oh My…

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