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 0.100 kg mass is used. What is the spring constant of the spring in N/m? Today’s Objective – Single and Double slits

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

Single and Double Slit Review

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.

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

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.

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 9.2-3 p 364 #14-16 and p374 #17-26 What’s next? (What to read to prepare for the next class) Read Ch 9.4 - 9.5, p376 - 388