## Diffraction and Interference Lab

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Nathan Lindquist

Diffraction and Interference Lab

A. Single slit

1. As the width of the single slit increases, describe how the intensity pattern changes.

The distance between the maxima decreases, and the width of the maxima decreases. The central maximum becomes less intense, but the intensity decreases more gradually.

2. Describe how the intensity pattern changes from the red laser to green laser.

For the green laser, the maxima were more closely spaced, and the central maximum was narrower.

B. Double slit

1. Compare the intensity pattern to that of a single slit.

The intensity of the maxima drops of faster, but the maxima are wider than they are for a single slit.

2. Describe how the intensity pattern changes as the width of the double slit increases.

As the gap gets wider, the central maxima gets brighter, but the distance between maxima decreases.

Describe how the intensity pattern changes from the red laser to the green laser.

For the green laser, the maxima were narrower and closer together than they were for the red laser.

C. Diffraction grating

1. Compare the intensity pattern of the diffraction grating to that of the double slit. Why is the diffraction grating better for making accurate determinations of wavelength?

The distance between the maxima is much larger when using the diffraction grating, so it is easier to get an accurate measurement of the distance between maxima.

2. As the spacing of the diffraction grating increases, describe how the intensity pattern changes.

The maxima get closer and closer together.

3. Describe how the intensity pattern changes for a green laser.

The maxima are closer together, and the maxima are narrower than they are for a red laser.

D. Calculate wavelength of red laser

Data:

530 grooves/mm

Distance to wall = .975 m

Distance between maxima = .358 m

Calculations:

Theta = arctan(.358 m / .975 m ) = 20.2 degrees

D = 1 mm / 530 grooves = 1.89e-6 m

Wavelength of red laser = dsin(theta) = (1.89e-6 m)(sin 20.2 degrees) = 650 nm

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