A red helium-neon laser was used to project a diffraction/interference pattern o

Question

A red helium-neon laser was used to project a diffraction/interference pattern on a screen mounted a distance of 1.20 m from the element(s) producing the pattern. Using positive values to indicate distances to the right of the center of the central bright spot on the observing screen and negative values for distances to the left of the center, the following data were taken: Was this pattern produced by a single -slit or a double -slit? Explain your reasoning in detail. Calculate the slit width or center to center spacing of the slits as appropriate. By some appropriate method estimate the uncertainty of your calculated value.

Explanation / Answer

This pattern is produced by double slit .

If one illuminates two parallel slits with a more intense red laser, the light from the two slits again interferes. Here the interference is a more pronounced pattern with a series of light and dark bands. The light is always found to be absorbed at the screen at discrete points, as individual particles , the interference pattern appearing via the varying density of these particle hits on the screen.

Here, d * sin(theta) = n * lambda               (For maxima)

=> d * (y/D) = n * lambda

=>   d * (0.017/1.20) = 1 * 632.8 * 10-9

=> d = 0.04466 mm

=> centre to centre spacing of slits =   0.04466 mm

uncertainty of calculated value =   0.0234 * 10-2 mm

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