PHENOMENA OF LIGHT

Chapters 27, 29, & 31

Easy to get mixed up…

Polarization (Light) Ch 27

Reflection (Water & Light) Ch 29

Refraction (Light) Ch 29

Dispersion (Rainbows) Ch 29

Total Internal Reflection (TIR) Ch 29

Diffraction (Water & Light) Ch 31

Interference (Water & Light) Ch 31

Thin Film Interference (Oil in the Gutter) Ch 31

LASERS (Monochrome & Coherent) Ch 31

Polarization

Intensity varies as polarizer is rotated

Courtesy Siltec Ltd.

Polarization

                                                                        

Courtesy of 3M Corporation

In linear Polarization light vibrations become confined to a single linear plane

Propagation of a Linearly Polarized Electromagnetic Wave

               

Animation Courtesy Siltec Ltd. http://www.infoline.ru/g23/5495/Physics/English/feedback.htm

Reflection

Light bounces off objects

Consider “rays” – light moving in straight line

Law of reflection: angle of incidence = angle of reflection

Law of Reflection i = r

I - incident ray

R - reflected ray

N – normal

Theta-I is angle of

incidence

Theta –R is angle of

reflection

How Curved Mirror Forms Real Images

Refraction: How Much Does It Bend

Angle of incidence i

Angle of

refraction r

Snell’s Law:

ni sin i = nr sin r

Helpful Analogy:The Band of Sand

What happens when a car drives into the sand?

highway sand

Which way does the car turn?

Toward and Away from Normal

When light enters a more dense (greater n) medium, it bends toward the normal

When light enters a less dense (smaller n) medium, it bends away from the normal

Index of Refraction

Ratio of speed of light in vacuum to speed of light in material

n = c/v = 3.0 x 108 m/s/vn always greater than one

Dispersion

Spreading of white light into spectrum of wavelengths

Why Dispersion Occurs

Index of refraction, n, depends on wavelength Typically n decreases as increases

Exit angle from prism depends on

White light

Forming a Rainbow

Way Complex Applet …

Java Applet

Total Internal Reflection

Fiber Optics – NOT just

Light but

INFORMATION

Diamonds – very bright!!

Diffraction

Bending of Light around an obstacle, a corner or a slit

Predict This

What happens when a beam of light goes through two tiny slits?

What pattern do you expect on the screen beyond?

Double Slit Interference Applet

What if light from two slits interferes?

http://www.ece.gatech.edu/research/ccss/education/Java/1998.Winter/Projects/pierce-woods/project/bin/projApp.htm

Experiment performed by Young in 1801

Convincing evidence for wave nature of light

Another Double Slit Applet (Not at this time)

Varying the Slit Separation

Courtesy of Siltec Ltd. http://www.infoline.ru/g23/5495/Physics/English/feedback.htm

Single Slit Interference

Also called diffraction

Fringes are larger

Size of fringes decreases out from center of pattern

Derivation, not

Single and duel with sound and a listener

http://phet.colorado.edu/new/simulations/sims.php?sim=Sound

More On Single Slit Interference

Pattern dominated by central maximum

Called central diffraction maximum

Width measured from minimum to minimum

Twice as wide as other fringes

Much brighter than other fringes

http://phet.colorado.edu/new/simulations/sims.php?sim=Wave_Interference

Single Slit Diffraction- Varying the Slit Width

Fringes get bigger as slit gets smaller

Diffraction Gratings

Diffraction Grating has thousands of lines per cm cut into glass plateLight from each slit interferes with light from all other slitsAnalysis like Double SlitSin = m/d principal maxima (bright)Lines very close so maxima occur at large anglesis maximum possible so only a few maxima (“orders”)exist

Spectrum Produced by Grating

Thin Film InterferenceLet film thickness = t

Assume no net phase change on reflection

2t = mm

Condition for bright

2t = (m+1/2)

Condition for dark

For one hard reflection 2t =mbecomes condition for dark

Examples of Thin Film Interference

Oil on Water

Soap Bubbles

Anti-reflective coating on lens

LASERS

Big and Small