Chapter 25 Notes
College Physics by Giambattista et al.
Physical Optics
 theory of how light moves as a wave
Interference – how waves overlap (general phenomenon)
CONSTRUCTIVE
in phase, “bright”
DESTRUCTIVE
completely out of phase, “dark”
IN BETWEEN
partially out of phase, “gray”
Path difference
Δℓ = 0, λ, 2λ, 3λ, …
 3 5
,
= ,
,...
2 2 2
constructive
destructive
Young’s Two-Slit Experiment
y
d
θ
D
Δℓ
Path difference
d sin θ = 0, λ, 2λ, 3λ, …
 3 5
,
= ,
,...
2 2 2
John B. Ross, Ph.D.
constructive
destructive
IUPUI Physics Dept.
Chapter 25 Notes
Note that
College Physics by Giambattista et al.
tan  
y
D
Diffraction
 wave bending around corners, through holes, etc.
Diffraction effects are pronounced whenever λ ≤ a (width of aperture)
Question: why can you hear around a corner but not see around a corner??
Single-Slit Diffraction
θ
central
max.
a sin θ = λ, 2λ, 3λ,… dark fringes only
Gratings – color separators
0) Reflection – demo: CD
0) Refraction – demo: laser amazer goggles
Refraction grating condition
d sin θ = 0, λ, 2λ, 3λ, … maxima only
Gratings are rated by their # of slits per cm, N. Suppose you have 5000 slits/cm, then
d = 1/N = 2×10–4 cm = 2 μm.
John B. Ross, Ph.D.
IUPUI Physics Dept.