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Lecture 27
Thin LensesDiffraction
Problems due Wednesday
• 17: 13, 17, 19, WB 25: 1-9• 13: diffraction grating• 17: ditto• 19: skip b• WB: 1-9 pictures of interference
Thin lenses
• A brief detour to cover a topic needed for lab this week.
object
image
s
s’
Converging lens
f
1 1 1 ' '
'
h sm
s s f h s
h
h’
Two Lenses
• The image formed by one lens can be the object for the second lens. For the second lens, s2 is the distance from the image formed by the first lens and the location of the second lens.
• f>0 for a converging lens, the only kind we will deal with in lab this week.
Review of Friday
• Electromagnetic wave
Electromagnetic Waves
Slide 25-33
Sinusoidal Waves
• Single frequency (single color) and single wavelength, λ.
• TRANSVERSE with B and E perpendicular to the direction of motion.
• In vacuum velocity = c = 3.00 x 108 m/s• Right hand rule relates E, B and direction of
propagation–E = cB
Sinusoidal Waves Continued
• Wave traveling in the +x direction with E polarized along the y-axis, and hence B along the z-axis.
0
0
0 0
( , ) sin 2
( , ) sin 2
y
z
x tE x t E T
x tB x t B
T
E cB
Polarization
Slide 25-37
Two slit interference
• Young demonstrated light behaved as a wave.• Bright fringes occurred at angles
• For small angles
sin mm d
0,1,2,3,...
m
m
m
dm L
y md
Example
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
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
Problems due Today
• 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 y5 – y1, find λ• 10: two slits given fringe spacing, λ• 12: Δr
Problems due Wednesday
• 17: 13, 17, 19, WB 25: 1-9• 13: diffraction grating• 17: ditto• 19: skip b• WB: 1-9 pictures of interference
