# Lecture 28, Wednesday April 15 Diffraction Grating Thin Film Interference Single Slit Diffraction.

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Lecture 28, Wednesday April 15 Diffraction Grating Thin Film Interference Single Slit Diffraction

Problems due Today 17: 13, 17, 19, WB 25: 1-18 13: diffraction grating 17: ditto 19: skip b WB 17: 1-9 pictures of interference 25: 19, 22, 28, 29, 31

Two slit interference Young demonstrated light behaved as a wave. Bright fringes occurred at angles For small angles

QUIZ # 9 Two narrow slits 0.04 mm apart are illuminated by light from a HeNe laser (λ = 633 nm). A. What is the angle of the first (m = 1) bright fringe? B. What is the angle of the thirtieth bright fringe? Slide 17-11

Index of Refraction—cf. Lab last week Index of refraction

The Diffraction Grating Slide 17-12

The Intensity Pattern Due to a Diffraction Grating Slide 17-14

The Fringes Become Very Narrow as the Number of Slits is Increased Slide 17-15

A Diffraction Grating Splits Light into the Wavelengths That Make It Up Slide 17-16

All waves spread out after passing through a small enough gap in a barrier. This phenomenon is known as 1.Antireflection 2.double-slit interference 3.Refraction 4.diffraction

Problems due Friday 17: 1, 2, 4, 7, 9, 10, 12 2: speed in glass 4: wavelength in glass 7: two slit interference 9: ditto, given d and y 5 – y 1, find λ 10: two slits given fringe spacing, λ 12: Δr

Problems 25: 19 E = 10 V/m in an electromagnetic wave. What is B? 22: – What is λ, f, and electric field amplitude? 28: I = 10 W/m 2 for a linearly polarized wave. Intensity through polarizer with b) θ = 30 0 ?

More Problems 29: 25% passes polarizer. Angle of polarizer with respect to electric field? 31: Unpolarized light with I = 350 W/m 2 – What is I after two polarizers with second axis 35 0 to axis of first?

Problems 17 CQ1: frequency in water, glass CQ3: change in λ n, does it change apparent color? MC17: what changes when light enters glass? 1: travel time through piece of glass

Thin-Film Interference Slide 17-17

Phase Changes Due to Reflection Slide 17-18

Analyzing Thin-Film Interference Slide 17-19

Single-Slit Diffraction Light passing through a narrow slit spreads out beyond the slit. Slide 17-23

Analyzing Single-Slit Diffraction Slide 17-24

Single-Slit Diffraction: Positions and Intensities Slide 17-25

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