Huygens Principle

1
Huygens Principle
All points on serve as point source of spherical
secondary wavelets. After a time t, the new
position of the wavefront will be that of a
surface tangent to these secondary wavelets.
2
Derivation of the Law of Refraction
Time of travel from e to c
Time of travel from h to g
3
Wavelength, Frequency in a Medium
In a medium with an index of refraction n,
Frequency
The frequency of the light in the medium is the
same as it it in vacuum.
4
Phase Difference
Phase difference between two light waves can
change if the waves travel through different
materials.
Number of wavelengths in medium 1, N1
Number of wavelengths in medium 2, N2
5
Diffraction
6
Youngs Double Slit Experiment
Max bright fringes, bright bands, maxima Min
dark fringes, dark bands, minima
7
Youngs Double Slit Experiment
?Ldsin?
8
Rules of Reflection
9
Rules of Reflection
10
Interference From Thin Filmn1 ltn2ltn3
L
Path difference 2L
Maxima
Minima
m0, 1, 2, 3,...
11
(a) For which situations does reflection at the
film interfaces cause a zero phase difference for
the two reflected rays?
(b) For which situations will the film be dark if
the path length difference 2L causes a phase
difference of 0.5 wavelength?
12
A thin film of acetone ( n1.25) coats a thick
glass plate (n1.50). White light is incident
normal to the film. In the reflections, fully
destructive interference occurs at 600 nm and
fully constructive interference at 700 nm.
Calculate the thickness of the acetone film.
13
A broad beam of light of 683 nm is sent directly
downward through the top plate of a pair of glass
plates. The plates are 120 nm long, touch at the
left end, and are separated by a wire of diameter
0.048 mm at the right end. The air between the
plates acts as a thin film. How many bright
fringes will be seen by an observer looking down
through the top plate?
14
Michelsons Interferometer
15
Interference From Thin Filmn1 gt n2
L
Path difference 2L
Maxima
Minima
m0, 1, 2, 3,...