1. Phy2005 Applied Physics II Spring 2017 Announcements:
HW Solns Chs posted
Exam III April 10 in-class
Reviews Today 4pm NPB 2205 (upstairs)
Sunday April 10 4pm NPB 2205
Coverage: Chs

2. Maxima or minima of intensity depend on difference in the
Last time
We know light is a wave because of interference phenomena:
Interference patterns with 2 coherent sources
Maxima or minima of intensity depend on difference in the
path length from the 2 sources to the observation point

3. Last time s1 s2
• P r1 r2
|r1 – r2| = 0, l, 2l, 3l, …, ml (m: integer)  Constructive Int.
|r1 – r2| = l/2, 3l/2, 5l/2, …, (2m+1)l/2  Destructive Int. l

4. Last time ml (0, ±l, ±2l, …) Constructive dsinq =
(m+1)l/2 (±l/2, ±3l/2,…) Destructive d h q x 1 2 3
2nd-order bright fringe
1st order bright fringe

5. Interference in thin films
Ds =
Difference in two routes +
= 2x
(when qi << 1)
Half –reflecting planes
2x = ml constructive
= (2m+1)l/2 destructive x x q
For an arbitrary angle q
Ds = 2x/cosq

6. Ex. 1 The optical flat is a device used to measure the smoothness
or flatness of surfaces. Two optical flats are illuminated by 580 nm
light. A narrow, wedge-like gap between them gives rise to the fringes
as shown. The distance between the fringes is 0.6 cm. Find the angle
of the wedge assuming the gap is filled with (1) air and (2) water. q d x2 x1 L
2x1 = ml
2x2 = (m+1)l
tanq = d/L = l/(2L)
2(x2 – x1) = l = 2d  d = l/2
tanq = 580 x 10-9/(2 x 0.006)
tanq = 436 x 10-9/(2 x 0.006)
For air, l = 580 x 10-9 m
For water, l = 580 x 10-9/1.33 = 436 x 10-9 m
q=0.0028o(air), (water)

7. Clicker Quiz Time Log in your remote! ACADEMIC HONESTY
Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions.
Log in your remote!

8. Q1: A thin film of polymer used in an antireflective coating
has an index of refraction of If light of wavelength%
545nm is incident on the film, but is found to be
entirely transmitted and not reflected, what is a possible
thickness x of the film (in m)?
9.1 x 10-8
1.8 x 10-7
1.3 x 10-7
(4) 0
(5) 3.6 x 10-7 x n

9. Dr = dsinq = ml  Constructive
Diffraction Grating
provides much clearer and sharper interference pattern
and a practical device for resolving spectra.
Dr = dsinq = ml  Constructive q d

10. Huygens’ principle construction

11. Q. A diffraction grating having 20,000 lines per inch is illuminated
by parallel light of wavelength 589 nm. What are the angles at
which the first- and second-order bright fringes occur?
dsinq = ml
d = /20000
= 1.27 x 10-6 (m)
First-order sinq1 = ml/d
= 589 x 10-9/1.27 x 10-6
= 0.464
q1 = 27.6
Similarly, sinq2 = 2 x 0.464
= 0.928
q2 = 68.1