Lab 12

TA: Keslo Estil SEC#: Name:

Lab 12. Double-Slit Interference

Until the beginning of the 19th century, the question of whether light propagated as a type of wave, or as a beam of particles had not been answered. Newton favored the particle theory to explain why light appeared to travel in straight lines, whereas Robert Hooke and Christian Huygens were able to explain refraction by assuming that light traveled as a wave with different speeds in different media. Then in 1801, Thomas Young performed his crucial two-slit interference experiment, which clearly demonstrated the wave nature of light.

In Young’s experiment, light waves of wavelength spread out from each slit by a process called diffraction as shown in Fig. 1. Along the directions where the crests reinforce each other, as indicated by the solid lines, the wave intensity is high. Along the directions where a crest is cancelled by a trough, as indicated by the dashed lines, the intensity is low. If a screen is positioned to intercept the waves, an interference pattern of bright and dark "fringes" is obtained. The condition for maximum brightness at a point on the screen is that the distances from the slits to that point differ by a whole number of wavelengths, m, where m is an integer. The distance y between the centers of two adjacent bright fringes is given by equation 1 in Fig. 1.

Objectives

In this experiment, you will:

· Compare the patterns of light produced by a single slit and by two slits side-by-side.

· Investigate how the spacing between adjacent fringes depends on the spacing between two slits, and on the wavelength of light being used.

· Determine the wavelength of light from the two-slit pattern and compare it with the wavelength of the laser light source.

Preliminary Question (1-4)

Evaluation of Data (1-7)

Analysis (1-8)

Note: Show all equations, calculations and very clear screenshot of the graphs with fit to receive full credit.

Data Tables

Double-Slit with green laser
Slit Separation, d	1/d	Fringe Separation, y
0.0125 cm
0.025 cm
0.05 cm
0.075 cm

Slits to screen distance, L = 50 cm

Calculated wavelength of green laser = [ANS] nm

Wavelength printed on red laser = 532 nm

Percentage difference = [ANS] %

Slit Separation, d	1/d	Fringe Separation, y

Slits to screen distance, L = 50 cm

Calculated wavelength of red laser = [ANS] nm

Wavelength printed on red laser = 650 nm

Percentage difference = [ANS] %