The Nature and Propagation of Light Chapter 33 The Nature and Propagation of Light

Reflection and Refraction

Reflection

Reflection We will focus on specular reflection

The Law of Reflection All angles are measured with respect to the normal. normal

Multiple reflections

The image

Where is the image? Trace at least two light rays. The image is at where the rays meet. Bring a protractor to class and quizzes and exams.

Where is the image? Trace at least two light rays. The image is at where the rays meet.

Finding the image

Image with multiple reflections

Snell’s Law of Refraction

Refractive Index

Useful facts

Reflection and refraction

Be careful with the normal

More on refractive index

Find the refractive index and the speed of light in the liquid

Solution

Different colors different speed

Dispersion

What happened to my ruler?

Explanation

How to catch a fish

How to catch a fish

The image

How to catch a bug

Find θair for the following cases: θwater θair 40° 47° 48° 48.75° 50° nwater = 1.33

Solution θwater θair 40° 58.7° 47° 76.6° 48° 81.3° 48.75° 89.4° 50° [Error] Total internal reflection

Total Internal Reflection

A slightly more accurate picture

Total internal reflection (TIR) Total internal reflection occurs when θincident > θc. It is when all the refracted light disappear and all the light got reflected back.

The critical angle, θc θc is the angle of incident θincident when θrefraction = 90o

Wrong Answers! Define critical angle: Critical angle is when TIR happens. (Is what???) Critical angle is the angle of incidence when TIR happens. (TIR happens for many values of θincidence) Critical angle is the angle when TIR begins. (Which angle???) Define TIR: TIR is when the the angle of incidence = critical angle. (What about θincidence>θc?) TIR is when the the angle of incidence > critical angle. (Circular logic)

Find the critical angle for diamond in air

Shiny diamonds and total internal reflection

Cubic Zirconium Refractive index: 2.15 to 2.18 (diamond: 2.42) Hardness: 8.5 to 9 (diamond: 10) Ingredients: zirconium oxide, magnesium, calcium (diamond: carbon)

Applications of TIR Fiberoptics

Total internal reflection

Polarization

Polarizing Filters Electrons on long polymers (long molecules) that moves only in one direction, hence absorbing energy of the E field in that direction, but let the other direction through.

Two filters

Intensity Rules for Polarizer Make sure you know whether the light is polarized or unpolarized!

Example with two filters

Polarization by Reflection At the Brewster angle (or polarizing angle) θp, the reflected beam becomes polarized.

Brewster’s Angle Complete polarization by reflection occurs when the reflected beam is perpendicular to the refracted beam.

Brewster’s Angle Pictures taken with polarizers at different angles. The picture on the right has the reflected light removed by the polarizer to minimize reflection.

Polarization by Scattering

Circular and Elliptical Polarization

Circular Polarization

Wavelength in different medium

Huygen’s Principle Every point of a wave front may be considered the source of secondary wavelets that spread out in all directions with a speed equal to the speed of wave. The final wave is the sum of all these secondary wavelets.

Deriving Snell’s Law of Refraction

Principle of Least Time Light always travels between two points in the path that takes the least amount of time.