Daily Work Organizer Friday Question of the Day: How does interference create Nodes and Antinodes? Do Now: Agenda: Cornell notes Pre-lab Homework Homework: Pre-Lab pg Homework: Pre-Lab pg Constructive or Destructive interference?

Vocab WordPicture that reminds you of definition DefinitionWord or words that remind you of definition Sentence using word Constructive Interference Can create Maxima Build Amplitudes add together Can create Maxima Build Amplitudes add together Occurs at any location along the medium where the two interfering waves have a displacement in the same direction. Constructive interference between 2 waves can create maxima or antinodes.

Vocab WordPicture that reminds you of definition DefinitionWord or words that remind you of definition Sentence using word Destructive Interference “Minima” Destroy Amplitudes subtract Resulting wave is smaller “Minima” Destroy Amplitudes subtract Resulting wave is smaller Occurs at any location where two interfering waves have amplitudes in opposite directions.

New Tardy Policy FIf you’re tardy, more than once in a week, you lose 2 points from your grade.

It’s what we see… Wave Phenomena

Wave Interference Two wave sources near each other will create an interference pattern Lines made from constructive interference are called antinodes or maxima Lines made from destructive interference are called nodes or minima (no waves)

What does it look like?

Constructive Interference Sources in phase On some lines there are parts where crests overlap crests Waves are out of step by one wavelength S1S1 S1S1 S2S2 S2S let’s count the difference in wavelengths

Destructive Interference Sources in phase On other lines crests overlap troughs Waves are out of step by one half wavelength S1S1 S1S1 S2S2 S2S let’s count the difference in wavelengths

Interference counting waves on the interference pattern

Interference counting waves on the interference pattern

2 minutes FAnswer the questions on your Cornell notes!

1. At which of the labeled point(s) would constructive interference occur? 2. How many of the six labeled points represent anti-nodes? 1. At which of the labeled point(s) would constructive interference occur? 2. How many of the six labeled points represent anti-nodes? A & B 2

Lets Start the Pre-Lab! ~ 5 minutes

1.Purpose of lab: to _______________ 2.Hypothesis: what do you expect to see and why? 1.Purpose of lab: to _______________ 2.Hypothesis: what do you expect to see and why? The purpose of this lab is to recognize constructive and destructive wave interference patterns and use these patterns to calculate the wavelength of the waves causing this pattern When a crest and trough of two waves overlap I expect to see: When the crests of two waves overlap I expect to see: Constructive interference => antinodes Destructive interference => nodes

Hypothesis: what do you expect to see and why? When the distance between the 2 sources of waves increases I expect the distance between the nodes to ____________ because… When the wavelength increases I expect the distance between the nodes to ____________ because… When the distance between the 2 sources of waves increases I expect the distance between the nodes to ____________ because… When the wavelength increases I expect the distance between the nodes to ____________ because…

To Part I of the lab! pg. 204

Calculating wavelength Wavelength can be calculated from measurements on a point on an antinode λ λ

Calculating wavelength L= length from point to midpoint between sources x= perpendicular distance from point to central antinode d= distance between sources m= antinode number (central is m=0)

Wavelength can be calculated with the formula note: or: we can rewrite eqn as: Calculating wavelength

Which this in mind… find the wavelength of a wave! pg 207 Answer the questions on pg 210 when you finish

Which this in mind… find the wavelength of the wave in question 1 pg 210 Continue onto question 2 and 3 when you finish

To Part II of the lab! pg. 207

Changing d let’s look at the effect of changing the distance between the sources: d

Changing d let’s look at the effect of changing the distance between the sources: d An increase in d makes nodes closer together

Constructive Interference

Changing wavelength let’s look at the effect of changing the wavelengthchanging the wavelength note: larger λ means slower f

Diffraction Particles are blocked by barriers But waves can bend around the edges

Diffraction Effects of wavelength and slit size Larger wavelength means more diffraction Larger slit size means less curve

Diffraction Compare UHF (smaller) to VHF (larger) TV waves UHF waves slightly diffract below roof

Diffraction Compare UHF (smaller) to VHF (larger) TV waves VHF waves diffract much more would this house get all the channels?

Diffraction Which direction are the waves flowing?

Light Diffraction Newton originally thought light was a particle Thomas Young challenged the idea He used diffraction to test for light being a wave Two slits created an interference pattern

Light Diffraction This interference pattern can displayed on a screen The diffraction pattern is seen as fringes Dark spots are nodes, bright spots are antinodes

Light Diffraction Changing d and wavelength affect this pattern the same as they had the full interference pattern Proof that light is a wave

Diffraction All waves can bend around edges Colorλ interval infrared>700 nm red635 – 700 nm orange590 – 635 nm yellow560 – 590 nm green490 – 560 nm blue450 – 490 nm violet400 – 450 nm ultraviolet<400 nm

Thin Film Interference Each edge of a film can also be a wave source

Thin Film Interference When light hits a thin film… some light reflects off surface… thin film

Thin Film Interference Some light refracts through… then reflects off bottom surface thin film

Thin Film Interference These two rays then interfere with each other Closed ended reflections thin film

Thin Film Interference The phase change determines the type of interference Thin film interference equations creating or blocking colors example

Time to practice Go to pg. 222

Polarized Light Light is a transverse wave The wave below shows how this would appear If we looked at this wave head on it would appear as a line going up and down

Visualizing Polarized Light Light is a transverse wave The wave below shows how this would appear If we looked at this wave head on it would appear as a line going up and down

Unpolarized Light Naturally occurring light has waves on all planes This type of light is called unpolarized light

Polarized Light Naturally occurring light has waves on all planes This type of light is called unpolarized light Polarized light is made of waves vibrating only on one plane

Drawing Polarized Light Let’s imagine unpolarized light in just two planes of vibration Vertical wave drawn as an arrow Horizontal wave drawn as a dot

3 Methods of Polarization Selective Absorption Reflection Double Refraction

Selective Absorption A film of molecules stretched out in same direction These molecules absorb all the light in that plane Remaining 50% (perpendicular to molecules) passes through 2 filters lined up 90° to each other block 100%

Reflection method: Glare! The horizontal component of light tends to reflect off transparent surfaces (glare) The vertical component of light tends to refract Not a perfect polarization

Reflection When the reflected ray and the refracted ray are 90° from each other… They are both totally polarized

Polarizing Sunglasses Polarized sunglasses only block light that is vibrating horizontally (the glare) Real polarizing sunglasses will not work if you turn your head

Double Refraction Vertical component and horizontal component refract differently This gives two separate polarized rays

Double Refraction All light is blocked out with two selective filters One blocks out the horizontal the other the vertical Stress lines shown through double refraction