1. Physics 3 – Nov 3, 2016 P3 Challenge –
The equation of motion for the oscillation of a mass on a spring is given by y=(3.2 cm) cos (0.45 t) when a kg mass is used. What is the spring constant of the spring in N/m?
Today’s Objective –
Single and Double slits

2. Objectives/Agenda/Assignment
9.2 Single slit
9.3 Double Slit
Agenda:
Multiple slits
Thin films
Assignment: p 364 #14-16 and p374 #17-26

3. Single and Double Slit Review

4. Multiple slits Intensity of peaks increases by (N/2)2
N = the number of slits
Peaks of interference become sharper
N-2 number of secondary maxima appear between the primary maxima
Secondary maxima, get relatively smaller and smaller until they become negligible.
Diffraction gratings with large N create a sharp image of primary maxima
Notice we still see the diffraction envelope created by the slit width.

5. Thin Films
When light reflects off a substance with a higher index of refraction there is a 180° phase shift
This phase shift combines with the conditions of constructive and destructive interference to switch the results.
Ordinarily:
Constructive: path diff = (m) λ
Destructive: path diff = (m+1/2) λ

6. Thin Films
For thin films, the path difference is 2d and the wavelength of the light within the film is λ/n. Therefore:
With the phase change:
Constructive: 2dn = (m+1/2) λ
Destructive: 2dn = (m) λ
With no or two phase changes
Constructive: 2dn =(m) λ
Destructive: 2dn = (m+1/2) λ
n is the index of refraction, m is an integer and λ is the incident wavelength, d is the thickness of the film.

7. Exit slip and homework
Exit Slip – What is the condition for constructive interference from a thin film of n=1.25 on the surface of glass with n=1.33 if it had a thickness of d?
What’s due? (homework for a homework check next class)
Finish p 364 #14-16 and p374 #17-26
What’s next? (What to read to prepare for the next class)
Read Ch , p