Pasco OS-8523 SLIT ACCESSORY Manuel d'utilisateur télécharger pdf (Page 12)

012-05880D Slit Accessory

EQUIPMENT REQUIRED

– track and screen from the Basic Optics System (OS-8515)

– Diode Laser (OS-8525)

– Multiple Slit Disk (OS-8523)

– white paper to cover screen

– metric rule

Purpose

The purpose of this experiment is to examine the diffraction and interference patterns formed by laser

light passing through two slits and verify that the positions of the maxima in the interference pattern

match the positions predicted by theory.

Theory

When light passes through two slits, the two light

rays emerging from the slits interfere with each

other and produce interference fringes. The angle

to the maxima (bright fringes) in the interference

pattern is given by

d sin

= m

(m =0,1,2,3,…)

where d is the slit separation,

is the angle from

the center of the pattern to the m

maximum,

the wavelength of the light, and m is the order (0

for the central maximum, 1 for the first side maxi-

mum, 2 for the second side maximum, . . . count-

ing from the center out). See Figure 2.1.

Since the angles are usually small, it can be as-

sumed that

sin

≈ tan

From trigonometry,

where y is the distance on the screen from the center of the

pattern to the m

maximum and D is the distance from the

slits to the screen as shown in Figure 2.1. The interference

equation can thus be solved for the slit separation:

d =

(m =0,1,2,3,…)

Figure 2.2: Single Slit Diffraction Envelope

Figure 2.1: Interference Fringes

screen

slit

central envelope

dotted line is diffraction envelope

m = 1

m = 0

m = 2

m = 3

m = 4

diffraction minimum

m = 1

m = 2

m = 1

m = 0

tan

Experiment 2: Interference from a Double Slit

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Pasco OS-8523 SLIT ACCESSORY Manuel d'utilisateur Page 12

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