1 From Last time… Diffraction grating Two-source interference: Diffraction = interference from many sources Week3HW on Mastering Physics due Fri. Sep. 18 Week2HW due Fri. Sep. 11 New topic: Diffraction only one slit, but “wide” • Interference-like pattern from a single slit. θ central width ~ 2 λ a For a slit: Long wavelength: wide pattern Short wavelength narrow pattern Thursday, Sep. 10 Physics 208, Lecture 3 3 Huygen’s principle • Huygen’s principle : each portion of the slit acts as a source of waves • These sources interfere according to path-length difference. Overlapping diffraction patterns • Two sources ->two diffraction patterns. • Width central max determined by aperture. • Larger aperture gives better angular resolution θ Angular separation • For a circular aperture (e.g. lens) θ min = 1.22 λ D 36” Lick refractor at UC-Berkeley Thursday, Sep. 10 Physics 208, Lecture 3 5 Large aperture -> good angular resolution θ min = 1.22 λ D D Diffraction from other objects • General effect • Clearest w/single wavelength Thursday, Sep. 10 Physics 208, Lecture 3 6 Light diffraction by pinhead
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From Last time… New topic: Diffraction only one slit, but ... · (reflection, refraction, absorption) What about diffraction? • Light really behaves as a wave • The concept
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From Last time…
Diffraction grating
Two-source interference:
Diffraction = interference from many sources
Week3HW on Mastering Physics due Fri. Sep. 18
Week2HW due Fri. Sep. 11
New topic: Diffraction only one slit, but “wide”
• Interference-like pattern from a single slit.
€
θcentral width ~ 2 λa
For a slit:
Long wavelength: wide pattern
Short wavelength narrow pattern
Thursday, Sep. 10 Physics 208, Lecture 3 3
Huygen’s principle
• Huygen’s principle: each portion of the slit acts as a source of waves
• These sources interfere according to path-length difference.
Overlapping diffraction patterns • Two sources ->two
diffraction patterns.
• Width central max determined by aperture.
• Larger aperture gives better angular resolution
θ
Angular separation
• For a circular aperture (e.g. lens)
€
θmin =1.22 λD
36” Lick refractor at UC-Berkeley
Thursday, Sep. 10 Physics 208, Lecture 3 5
Large aperture -> good angular resolution
€
θmin =1.22 λD
D
Diffraction from other objects
• General effect • Clearest w/single wavelength
Thursday, Sep. 10 Physics 208, Lecture 3 6
Light diffraction by pinhead
2
Thursday, Sep. 10 Physics 208, Lecture 3 7
Interference summary • Waves start in phase • Travel different distances (extra path length = δ) • No longer in phase when combined (Phase diff φ)