How many l between 1 & 2 ? How many l between 1 & 4? How many nodes are there below?

How is a standing wave formed?2 waves or pulses same speed, l, f, undergo superposition interfering at fixed points of constructive & destructive interference forming pattern.

Light

Light is a small part of the EM spectrum.All EM waves have the same behavior.

What is Light/EM waves2 Models

1) Particles/Photons Packets of energy

2) Electromagnetic Wavesenergy-carrying waves emittedby vibrating charges.

Light displays both types of behavior.

Light & all EM waves are transverse, non-mechanical waves.EM waves begin as motion of charged particles.

Electromagnetic Wave VelocityThe speed c is the same for all forms of EM waves in a vacuum of space.

It is ~ 3.0 x 108 m/s.

No mass can go the speed of light.

Nothing can go faster.

The velocity of EM radiation is almost the same in air as it is in space.

In other substances it travels more slowly.

Ex: The wavelength of a certain color of visible light is 429 nm. Using your table, determine the color of the light. v = lf. f = v/lFor light in air or vacuum, v = 3x108 m/s

Find f = 3x108 m/s=________________ 429 x 109m.f = 7 x 1014 Hz = violet.

Amplitude is related to the wave energy. So is frequency.

High Amplitude means bright.

Higher f = higher energy change in color.

The Electromagnetic Spectrum Waves become more energetic as the wavelength gets shorter (freq. gets higher)Radio Waves - communication Microwaves - used to cookInfrared - heat wavesVisible Light - detected by your eyesUltraviolet - causes sunburnsX-rays - penetrates tissueGamma Rays - most energetic

The Visible Spectrum

A range of light waves extending in wavelength from about 400 to 700 namometers.

QuestionsIs it correct to say that radio wave is a low-frequency light wave?

Is a radio wave also a sound wave?

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Behaviors of Light & (Other waves)

Reflection

We see things because they reflect or transmit light into our eyes:Physics Rules

Luminous objects generate their own light (the sun)

Illuminated objects reflect light (the moon)

Line of Sight The way you locate objects. You see a line from an object or image to your eyes (light from the object travels along this line to your eyes). You sight along the line.

Reflection of Light Rayincident ray hits new material, reflected ray bounces back. Reflected Ray Incident Ray

Normal line perpendicular to the mirror surface

Law of Reflectionincident angle Qi = Qr reflection angleQi angle between incident ray and normal

Qr angle between reflected ray and normal.

Specular Reflection &Diffuse Reflection

Diffuse Reflection obeys law of reflection.

Driving at night on a wet roadway results in an annoying glare from oncoming headlights.

Problem A ray of light is incident on a mirror with Qi = 20o. Using a protractor and ruler, sketch the incident ray, the normal to the surface, the reflected ray.

Label the angles.Sketch 5 wavefronts on the rays that show a wavelength of 1 cm.

Read 14-1 and 14-2 Light & Reflection

Hwk Packet Reflection

A ray of light hits a boundary between 2 different materials, state what behavior(s) it might exhibit at the boundary.

Refraction

A wave entering a new material will change its velocity.

This will result in a bending of the wave either toward or away from a perpendicular to the interface.

Law of Refraction - Snells LawA ray passing from a faster medium to a slowermedium bends toward normal. Qi greater than Qr.

What happens to l?

For light traveling from a slow medium to a faster one, the refracted ray bends away from the normal. The light coming off fish bends at water/air interface.

Light rays from the chest bend toward boundary btw water & air.

Refraction of sunlight allows us to see sun a few minutes after it has set below horizon.

Why do waves bend? Different Velocities between 2 medium

Amount of BendingThe amount of bending of light is dependent on the ratio of the speed of light in the two mediums.

The greater the Dv between the two materials, the greater the bend.

Absolute index of refraction, n, is the ratio of the speed of light in a vacuum to its speed in a medium.n =cn= index of refractionvv = velocity in mediumc = speed of light in vacuum - 3 x 108 m/s

Light in a vacuum has an index of 1 since:n = c/v= c/cn= 1

All other materials have velocity less than c, so n is greater than 1. Air is so close that n ~1.

1. The speed of yellow light in calcite is 1.97 x 108 m/s. What is the absolute index of refraction for calcite?

n = c v 3.00 x 108 m/s= 1.52 (no units) 1.97 x 108 m/s

A substance has an index of refraction n, of 0.67. What is wrong with this statement?All indices of refraction must be 1 since no substance can allow light to pass at a faster speed than c.

1. Light travels at 1.1 x 108 m/s in material X. What is the absolute index of refraction for material X.

2. What is the speed of light in Lucite?

3. Light travels at 2.66 x 108 m/s in Popalite . What is the index of refraction for Popalite?

Hwk Wave Diagrams.

Snells Law Law of RefractionRelates angle of incidence, angle of refraction and the 2 indices of refraction as well as velocity.n1sin q1 = n2sin q2 .

n1 = indx refrc med 1.n2 = indx refrc med 2.q1 = angle of incidenceq2 = angle of refraction

Variations of Snells Law

sin q1=v1 sin q2 v2 also n2 = v1 = l1 n1 v2 l2 . All in ref table.

1. A ray of light strikes crown glass from air at an angle of 30o from the normal to glass. What is the angle of refraction?

Hint: Use Snells Law

n1 sin q1= n2 sin q2(1.00)(sin 30) = (1.52)(sin q2)

sin q2 = 0.5= 0.33 1.52

q2 = 19o

2. A ray of light enters diamond from glycerol at an incident angle of 40o. Make a scaled sketch showing the:

Incident rayReflected RayRefracted Ray

(use Snells Law to calculate).

3. A ray of light travels from water into air. The incident angle is 40o.

Make a scaled sketch showing the:

Incident rayReflected RayRefracted Ray (use Snells Law to calculate).

What would happen if a ray of light traveled from corn oil into glycerol?Nothing!

No refraction or reflection.

Light will not change its velocity and cannot recognize the difference between the two!

Read 15-1Do p 567 prac prb (top) 1-3, bottom 1,2

And pg 587 #10, 11, 14.

When Light Rays travel from fast to slow:The refracted rays bend.

The angle of refraction:..

The wavelength in then new material:..

When Light Rays travel from slow to fast:The refracted rays bend.

The angle of refraction:..

The wavelength in then new material:..

Phet bending lightWhat happens when light passes from slow to fast & qi gets very large?.

At the boundary between 2 different materials the wave is partially:reflected AND partially refracted/transmitted.

Critical AngleWhen light crosses from slow to fast medium, it bends from normal

Critical angle is a Q1 occurs when refracted ray is parallel with boundary & most of the ray is reflected internally.

As qi gets larger, ray bends away from normal at greater & greater angle. Beyond critical angle = total internal reflection occurs.

WATERAIRLight SourceCritical AngleTotal Internal Reflection

Critical angle qc is the incident angle (q1) that causes q2 to=90o.So:n1sin qc = n2sin q2 n1sin qc = n2sin 90

3. A certain material has an index of refraction of 1.333. What is the critical angle for a light beam entering air from this material?

ni sin qi= n2 sin qr

but qi = qc & qr= 90o & n for air = 1

So (ni)sin qc= (1)(1).

qc= sin-1 (1/ ni) sin-1 (1/ 1.333)

qc=48.6o.

4. What is the critical angle for light entering air from diamond? DiamondAir2.42 sin qc = 1 sin 90qc = 24.4o

Note: As wave enters new material its frequency does not change. Frequency is the rate of the vibration of causing the wave. Since the velocity changes, then the wavelength must change to satisfy v =lf.

Beyond Critical AngleTotal Internal Reflection

Hwk Rd tx 15 3do 582 # 1 4 &

Write it all out including question, equations, etc. will be graded.

Applications & Effects of Refraction

Total Internal Reflection light can be made to internally reflect in a tube or pipe. None escapes.

Light Pipe

Fiber Optics

Light going from cool to warm air can refract and cause mirages because you sight along a line parallel to the ray.

Road Mirage

Light from sky bends up toward you in hot air. You sight down along line.Image appears to be on ground.

Dispersion

Dispersion polychromatic (white) light is separated into component colors.Special case of refraction.

Occurs b/c different l/freqs travel at dif v in materials other than empty space.

Different ls will be refracted/bent more than others.

Short ls (high fs) change velocity & are bent more than long ls.

Each l of light travels a different speed in the prism - each is refracted a different amount.

This is dispersion.

Which color/l is least refracted?

Which color/l is refracted least?

See ls

Red Light is affected least. It is the longest l, and lowest f.

Dispersive Mediums = ones in which waves of dif f/ls, travel at dif speeds.Ex: glass, water are dispersivevacuum is not dispersive.Polychromatic = many colorsex: white lightMonochromatic = one colorex: laser light.

Rainbows-dispersion in droplets

.For ray that hits high drops you see red at the top. Other colors pass above you.

Hwk Text bookPg 587 #27-29, 36

pg 588 # 27 - 30

Mechanical Universe Opticshttp://www.learner.org/resources/series42.html#

Huygens PrincipleModels wave propagation as if each point on wave front is a source of new circular waves (wavelets). The new wavefront is a line sketched tangent to the curved wavelets.

Every point on a wavefront serves as the source of spherical secondary wavelets, such that the wavefront becomes the envelope of these wavelets. The wavelets have the same frequency and speed as the original wavefront.

Huygens Principle Predicts Refractive Angle for wavefronts.

Huygens Animationhttp://www.sciencejoywagon.com/physicszone/lesson/otherpub/wfendt/huygens.htm

Huygens Principle Predicts Refractive Angle