Section: ______
Name: ______________________________
Section Instructor: ______________________________
Physics 2208, Spring 2009
1
Cornell University
Assignment 12: Quantum Physics II
Concepts:
laser
wave aspects of particles
de Broglie wavelength (
λ
=
h p
)
diffraction of electrons & other particles
electron microscope
Schrodinger’s equation
wave functions & probability density
quantization & standing waves
tunneling
LEDs & solar cells
Reading in text:
Chapter 38: Sections 57.
Optional: Sections 8, 9.
Chapter 39: Sections 19.
Chapter 40: Sections 13, 7, 8, 11, 12.
Chapter 41: Optional: Section 10.
Reading in lab manual:
Unit 12 Supplement: Devices Using pn Junctions—LEDs and Solar
Cells.
Some possibly useful values:
Description
Symbol & Value
speed of light
c
=
×
=
×
300 10
81
..
m/s
nm/s
7
Planck constant
h
=
×
⋅
×
⋅
−
−
6 63 10
414 10
34
15
.J
s
=
.
e
V
s
hc
hc
=
×
⋅
1240 10
3
.e
V
n
m
elementary charge
e
=
×
−
160 10
19
.C
electron mass
mc
e
kg
MeV
=
×
=
−
911 10
0511
31
2
proton mass
p
kg
MeV
=
×
=
−
167 10
938
27
2
.
neutron mass
n
kg
MeV
=
×
=
−
168 10
940
27
2
.
Assignment:
No quiz on Assignment 12.
Due in lecture on Monday April 27.
1. A semiconductor diode laser (like the ones you’ve been using in the Physics 2208 lab) has a
power output of 3.0 mW and a wavelength of 670 nm.
The diameter of the laser beam as it
exits the laser is about 1 mm.
(a) What is the average intensity of this laser beam?
How does this intensity compare with
the intensity of bright sunlight (about 1000
) and the intensity of radiation at a
distance of 10 cm from a 100 W lightbulb?
2
W/m
(b) How many photons/s are produced by this laser?
(c) The spreading or
divergence
of this laser beam can be estimated by assuming that it is
diffractionlimited
, i.e., that the beam spreads like the central bright spot in a diffraction
pattern from a circular aperture whose width is the beam’s initial width.
What is the
divergence angle
(fullangle width) of this laser beam, assuming it is circular in cross
section?
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 Spring '08
 AMADEURI
 Energy, Quantum Physics, Diffraction, Light, Cornell University, laser beam

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