Embed Size (px)
DESCRIPTION
Agenda. Monday Diffraction – Problems How small? How many? Tuesday Diffraction – Laboratory, Quiz on Interference Wed Review Fri Bonus Quiz. Basic Diffraction Formula. D x = m l (constructive) D x = (m+1/2) l (constructive) m integer Open question What is D x?. Multiple Slits. - PowerPoint PPT Presentation
Citation preview
Agenda
• Monday– Diffraction – Problems– How small?– How many?
• Tuesday– Diffraction – Laboratory, Quiz on Interference
• Wed– Review
• Fri – Bonus Quiz
Basic Diffraction Formula
• x = m (constructive)
• x = (m+1/2) (constructive)– m integer
• Open question– What is x?
Multiple Slits
• x = m (constructive)
• x = (m+1/2) (constructive)– m integer
• Open question– x = dsin
Equation vs. Experiment
Coherent, monochromatic Lightwavelength
Slits (Turned perp.)Rectangular
Screen
m
3
2
1
0
-1
-2
-3
dsin() = m
d
Examine Situation for Given LaserMeans: fixed
Coherent, monochromatic Lightwavelength
Slits (Turned perp.)
Screen
m
3
2
1
0
-1
-2
-3
dsin() = m
d
Range of possible d values?Given: fixed
Coherent, monochromatic Lightwavelength
Slits (Turned perp.)
Screen
m
3
2
1
0
-1
-2
-3
dsin() = m
d
Range of possible d values?Given: fixed
dsin() = m d = m / sin()
Anything related to range of d?Try big & small….
Range of possible d values?Given: fixed
dsin() = m d = m / sin()
How big can d be?Pretty big, m can range to infinity….If d is big, what happens to angle?sin() = m/d….Large slit spacing, all diffraction squeezed togetherInterference exists – just all overlaps – beam behavior
Large Distance(Assume large width…)
Coherent, monochromatic Lightwavelength
Slits (Turned perp.)
Screen
d
dsin() = m
Slit one
Slit Two
Range of possible d values?Given: fixed
dsin() = m d = m / sin() How small can d be?
Pretty small, m can be zeroHow about for anything but m = 0Smallest m =1d = /sin()d small when sin() big, sin() <= 1smallest d for m=1 diffraction: d = Replace: sin()=msin() = mimplies if d = , three diffraction spotsif d < , no diffraction (m=0?)
Range of possible d values?Given: fixed
Coherent, monochromatic Lightwavelength
Slits (Turned perp.)
Screen
m
1
0
-1dsin() = m
d ~
What Happens?
• Diffraction from spacing & width– Overlaying patterns, superposition
• 3 slits, all same spacing– Very similar to two slits
• Tons of slits, all same spacing– Refined interference. Focused maxima
• Move screen farther away from slits– Bigger angle/distance on screen
• Move light source, leave rest same– Nothing
ResolutionWhen can you identify 2 objects?
Coherent, monochromatic Lightwavelength
Slits (Turned perp.)
Screen
m
1
0
-1dsin() = m
d ~ w ~
Not Here…
ResolutionWhen can you identify 2 objects?
Begin with diffraction
Diffraction of light through a circular aperture1st ring (spot) sin() = 1.22/D Same setup idea as before
ResolutionWhen can you identify 2 objects?
Begin with diffraction
Diffraction of light around a circular block1st ring (spot) sin() = 1.22/D Same setup idea as before
Things that might cause diffraction rings…Pits/dust on glassesIris of your eyeTelescope LensRaindrops
Pretty Picture
Moon
Raindrop
What you see
Headlights
Resolved (barely) Unresolved
Issue
• How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work)
• sin() = 1.22/D
1.5 m
Small Angle sin() ~ tan() ~ [radians]
Issue
• How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work)
• = 1.22/D • = y/L• What is D?
1.5 m = y
Small Angle sin() ~ tan() ~ [radians]
L
Issue
• How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work)
• = 1.22/D • = y/L• pupil: D ~ 5 mm • What is ?
1.5 m = y
Small Angle sin() ~ tan() ~ [radians]
L
Issue• How close must a car be before you can tell it is NOT a motorcycle.
(assume both headlights work)• = 1.22/D • = y/L• pupil: D ~ 5 mm
• GREEN ~ 500 nm
• Calculation Time
1.5 m = y
Small Angle sin() ~ tan() ~ [radians]
L
Issue• How close must a car be before you can tell it is NOT a motorcycle.
(assume both headlights work)• = 1.22/D • = y/L• y/L = 1.22/D• L/y = D/(1.22)
1.5 m = y
Small Angle sin() ~ tan() ~ [radians]
L
= 500 nm
D = 5 mm
Issue• How close must a car be before you can tell it is NOT a motorcycle.
(assume both headlights work)• = 1.22/D • L/y = D/(1.22)• L = Dy/(1.22) = 12km ~ 7 miles• Little far, but not crazy far• aberrations blur image more here
1.5 m = y
Small Angle sin() ~ tan() ~ [radians]
L
= 500 nm
D = 5 mm
Agenda
• Monday– Diffraction – Problems
• Tuesday– Diffraction – Laboratory, Quiz on Interference
• Wed– Review
• Fri – Bonus Quiz
