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Homework #4: Wave/particle duality
Phys320 – Spring 2007 (Reshchikov)
p. 1
Problem 1
A beam of positrons (positron
≡
antielectron) travels at 0.001% the speed of light and impinges on a slit that is 1
µ
m
wide. Use modern units to find the angle
θ
between the center line and 3
rd
minimum of the resulting diffraction
pattern. How far away would you locate a detector so that the 3
rd
minimum is spaced 20 cm from the center line?
()
2
5
6
11
sin
,
where
= 3,
1000 nm,
and
1240 eV nm
242.7 nm
/
(0.511 10 eV)(10 )
3
3 242.7 nm
sin
sin
46.7
1000 nm
20 m
tan
19 m
tan
tan 46.7
na
n
a
hh
h
c
pm
v
mc
v c
a
yy
c
Lc
L
λθ
λ
θ
−−
==
===
=
=
×
×
⎛⎞
⎛
⎞
=
°
⎜⎟
⎜
⎟
⎝⎠
⎝
⎠
=⇒=
=
=
°
Problem 2
Electrons with
E
K
= 0.5 eV are directed at two narrow slits a distance
d
apart. If the angle between the central
maximum of the resulting interference pattern and the next maximum is to be 3º, what should
d
be?
With
E
K
= 0.5 eV, the electrons have wavelength
26
1240 eV nm
1.735 nm.
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This homework help was uploaded on 04/22/2008 for the course PHYS 320 taught by Professor Baski during the Spring '04 term at VCU.
 Spring '04
 Baski
 Physics, Work, Light

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