Introduction: When two waves intersect, meeting in the same space at the same time, they combine - adding together constructively (disturbing the medium more than the individual waves, amplifying their energy) or destructively (canceling out the influence of each individual wave and reducing the energy at their intersection). Electromagnetic waves are subject to such interference. In the double slit experiment, a single source of light passes through two narrow slits, splitting in two, as if generated by two coherent light sources. When the light from these two sources is projected on a screen, an interference pattern is observed with bright bands of constructive interference alternating with dark bands of destructive interference.

link: http://vsg.quasihome.com/interfer.htm

Simulation guidance: ? Note the three variables that can be controlled: Lambda (the wavelength [color] of light, d (the spacing between the slits), and L (the distance between the slits and the screen upon which the interference pattern is projected). ? Notice that when you change the wavelength (Lambda) the color of the wave fronts and patterns on the screen changes. ? As you operate the simulation, your goal is to count the number, n, of bright bands projected upon the screen. Although counting sounds simple enough, it can be challenging as bands appear on the far edges of the screen or disappear off the edges. ? The graph (on the far right of the simulation) shows the amplitude of the interference (the intensity of the two light sources interfering). The maximum of this intensity graph marks the center of the bright bands. You can use the graph to calculate fractions of a bright band on the edges of your screen. When the two bands at the edges reach their peak, then two half bands have joined the other bright bands in the middle of the screen. Using fractional bands at the fringes of your screen will let you calculate a more accurate n value.

Part 1 - Varying Wavelength Procedure: 1. Choose a slit distance and screen distance, these should remain constant for the rest of this part of the investigation. Change wavelength within the wavelength range and count the number of bright bands.

d = ___________ (mm) L = _______________ (m)

2 = (nm) L= (m) Slit Distance Range Slit distance (d) chosen # of Bright bands observed 2-2.5 mm 2.5-3.0 mm 3.0-3.5 mm 3.5-4.0 mm 4.0-4.5 mm 4.5-5.0 mma) W'hat is the trend for slit distance (d) and the number of bright bands? (Circle your responses) (2 pts) As slit distance (d) increases 4' decreases, the number ofbright bands increases 3' decreases. b) Is it a direct or inverse relationship? (Circle the correct response) (1 pt) Direct Inverse Screen distance (L) chosen it of Bright bands observed 2.0-2.5 m 3.0-3.5 m 3.5-4.0 m 4.0-4.5 m _ 4.5-5.0 m _ a) What is the trend for screen distance (L) and the number of bright bands? (Circle your responses) (2 pts) As screen distance (L) increases I decreases, the number ofbright bands increases it decreases. b) Is it a direct or inverse relationship? (Circle the correct response) (1 pt) Direct Inverse 4. Circle the variable(s) that are directly proportional to the number of bands, belonging in the numerator. Wavelength (A) Slit distance (11) Screen distance (L) (1 pts) 5. Circle the variable(s) that are inversely proportional to the number ofbands, belonging in the denominator. Wavelength (A) Slit distance (d) Screen distance (L) (1 pts) a) What is the trend for wavelength (2) and the number of bright bands? (Circle your responses) (2 pts) As wavelength (2) increases / decreases, the number of bright bands increases / decreases. b) Is it a direct or inverse relationship? (Circle the correct response) (1 pt) Direct Inverse