Wave Nature of Light

Review - Explain this.

E. Wave Nature of Light

2 Competing Theories:

1. particle	2. wave
	Wikimedia - (c) 2002 B. Crowell, GFDL licensed

Behavior of Light Supporting Wave Theory

1. Diffraction – light spreads out into the region behind an obstacle

MIT Tech TV

Review

What kind of wave behavior is demonstrated below?

School Blocks YouTube? Use the file below.

TuningBeatsYT.mov

St. Mary's Physics YouTube Channel

2. Interference – Young’s Double Slit - Late 1800's

Pattern created by a single light wave
passing through 2 small slits!

Claus_Jönsson_Interferenz.jpg‎
(146 × 200 pixels, file size: 1 KB, MIME type: image/jpeg)

Prof Dr. Claus Jönsson

Which letters show constructive interference?

destructive interference?

Move your mouse left and right over the simulation below

St. Mary's Physics

λ/d = x/L

St. Mary's Physics

λ/d = x/L

Monochromatic Coherent
Light Source was used

Which light source is coherent?

June 1997 Regents Test

Double Slit - Wavelength Difference-
Michael Fowler Flashlets

Name that interference / Wavelength shift?

Constructive

Whole Wavelength Shift

Name that interference / Wavelength shift?

Destructive

1/2 λ difference

| Larger |

St. Mary's Physics

If you draw a line from each slit to the 1st order bright line, you will notice that one line is longer than the other.

The difference between these two lines is 1λ.

Destructive Interference
1/2, 1 1/2, 2 1/2 ...
Wavelength difference

Constructive Interference

causes ...

Bright Lines

Destructive Interference

causes...

Dark Lines

AP Physics

Finding 2nd,3rd,4th
.... order bright lines

sinq = ml/d

q = angle between slits and line

d = distance between slits

m = 0, 1, 2, .... order bright lines

m = 1/2, 1 1/2, 2 1/2 dark lines

q = angle to bright line

x/L = ml/d

x = distance from central maxima

Polarization

AP Physics

Ex) Calculate the distance between two slits in a Double Slit Experiment if the wavelength of the light used is is 5 x 10^-7 m and the distance between the central maximum and the first order bright line is 2 x 10^-2 m. The distance from the slits to the screen is 4 meters.

λ/d = x/L

(5 x 10^-7 m)/d = (2 x 10^-2 m)/4 m

Answer d = 1 x 10^-4 m

Question: If they give you d, L and x and asked you to find the COLOR of the light used, What would you do? Where would you go to find the color?

Answer:

1. Solve for λ use Young's Equation

2. Use 3 x 10⁸ m/s = fλ to find the colors frequency

3. Look up the color on page 2 Ref.