1. You want to photograph a circular diffraction pattern whose central maximum h

Question

1. You want to photograph a circular diffraction pattern whose central maximum has a diameter of 0.9 cm. You have a helium-neon laser ( = 633 nm) and a 0.13 mm diameter pinhole. How far behind the pinhole should you place the viewing screen?

2. For a demonstration, a professor uses a razor blade to cut a thin slit in a piece of aluminum foil. When she shines a laser pointer ( =686 nm) through the slit onto a screen 5.2 m away, a diffraction pattern appears. The bright band in the center of the pattern is 8.0cm wide. What is the width of the slit?

3. The figure below shows the light intensity on a screen 2.9 m behind an aperture. The aperture is illuminated with light of wavelength630 nm.

(a) Is the aperture a single slit or a double slit?

(b) If the aperture is a single slit, what is its width? If it is a double slit, what is the spacing between the slits?

http://www.webassign.net/knight/p22-28.gif

4. Rank in order the following according to their speeds, from slowest to fastest (Use 1 as the slowest and 5 as the fastest).

425-nm-wavelength light through a pane of glass 500-nm-wavelength light through air 540-nm-wavelength light through water 670-nm-wavelength light through a diamond 670-nm-wavelength light through a vacuum

Explanation / Answer

1. We want the 1st minimum to be y = 0.45 cm from the center. This is similar to slit diffraction except an m-value of 1.22 is used instead of 1 . We set d = hole diameter (analogous to slit width).
= arcsin(m*lambda/(d)) = 0.34 deg
D = y/tan() = 75.83cm

2.  sin ~= tan = /d = x/2D
=> width of the slit, d
= 2D / x
= 2 * 5.2x 10^(6) * 686 x 10^-9 x 10^6 / 8 x 10^(4) µm
= 89.18 µm.

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