Review - Explain this.

St. Mary's Physics YouTube Channel

 

 

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

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

 

 

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.

 

 

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