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

m

 

d

sin 

m

• For small angles 

m



m



y m



d



d m

 0,1, 2, 3,...

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

n v

  

mat

speed of light in vacuum

f

speed of light in material

 

mat v f



c nf c

 

f



vac



vac n



c v

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

25% 25% 25% 25% A nt ir ef le ct ion d ou bl e sli t i n...

R ef rac tion d iff rac tion

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:

y



V m x

8

x

 2 

ft

) • – 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 color?

, does it change apparent 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