PASCO OS-8529 SLIT ACCESSORY - Manual (Page 7)

012–06348A Slit Accessory
3
Purpose
The purpose of this experiment is to examine the diffraction pattern formed by laser light
passing through a single slit and verify that the positions of the minima in the diffraction
pattern match the positions predicted by theory.
Theory
When diffraction of light occurs as it passes through
a slit, the angle to the minima in the diffraction
pattern is given by
where a is the slit width, θ is the angle from the
center of the pattern to the m th minimum, λ is the
wavelength of the light, and m is the order (1 for
the first minimum, 2 for the second minimum, .
. . counting from the center out). See Figure 1.1.
Since the angles are usually small, it can be
assumed that
From trigonometry,
where y is the distance on the screen from the
center of the pattern to the m
th minimum and D is
the distance from the slit to the screen as shown in
Figure 1.1. The diffraction equation can thus be
solved for the slit width:
a = m
λ
D
y
(m = 1, 2, 3,
…
)
sin
θ ≈
tan
θ
tan
θ
=
y
D
a sin
θ
= m
λ
(m = 1, 2 , 3,
…
)
Materials required:
• optics bench 1 • white projection surface
• Diode Laser (OS-8528) • metric rule
• Single Slit Set (OS-8529) • page 2 of the Slit Accessory manual
1 From the Introductory or Advanced Optics System (OS-8500 or OS-9254A)
Experiment 1: Diffraction from a Single Slit
θ
D
a
slit
screen
Figure 1.1: Single Slit Diffraction Pattern
m = 2
m = 1
m = 2
m = 1 y