Question

2-) A diffraction/interference pattern using a red helium-neon laser as a light source is observed on a screen 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 pattern on the observing screen and negative values for distances to the left of the center, the following data is taken :

Maxima(Cm) Minima(cm)

-6.60 -6.10

-5.40 -4.75

-4.30 -3.60

-3.00 -2.35

-1.80 -1.20

+1.70 +1.15

+3.00 +2.40

+4.20 +3.60

+5.50 +4.85

+6.65 +6.05

Identify this as a single-slit, double slit, or diffraction grating (multiple slut ) pattern, and calculate the slit width or center-to-center spacing of the slits as appropriate, explain your reasoning in detail.

Answer 1

This is a single slit phenomenon. The way to tell is by the minima. The first minima on either side of center are 1.15 and -1.20 the distance between those is 2.35 cm. The distance to the next minima on either side is 1.15 cm on the negative side and 1.25 on the positive side. Providing for a bit of experimental error, its clear to see that the distance between the first two minima on either side is basically twice the value of each successive minima. This only occurs in a single slit experiment.

The formula that applies here is y/L = m(wavelength)/a

I will take an average distance for all minima

On the negative side ...1.2, 1.15, 1.25, 1.15, 1.35

On the positive side ...1.15, 1.25, 1.2, 1.25, 1.2

Add them up and divide by 10 for the average = 1.215 cm

The red helium neon laser operates at 632.8 nm

(.01215)/1.2 = 1(632.8 X 10^-9)/a

a = 6.25 X 10^-5 m (That is 62.5 um)