Double Slit Interference Lab

Labib Haque SPH4U

Double Slit Interference Lab Purpose: The purpose of this experiment is to use the technique developed by Thomas Young in his double slit experiment to determine the wavelength of laser light.

Apparatus: 

Laser

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Double Slit Plate, Diffraction Grating

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Screen (A4 paper on the wall)

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Meter stick

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Ruler (accurate to mm)

Procedure: (refer to appendix A for full procedure of lab) Observation: Table 1 (below): Results from

Table 2 (below): Results from

d=0.132mm double slit experiment.

d=0.033mm double slit experiment

L= 2.25m

d= 0.132mm

delta x (cm)

Average (cm)

0.9

L= 2.25m

d= 0.033mm

delta x (cm)

Average (cm)

4.4

1.1

4.5

1.2

4.3

1.0

1.1

1.1

4.5

4.5

4.6

1.3

4.3

1.0

4.5

1.2

4.6

Analysis and Calculation Part 1 (Table 1) L=2.25m -4

D = 0.132mm = 1.32 x 10 m -2

Δx(avg)= 1.1cm = 1.1 x 10 m λ=?

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Labib Haque SPH4U

Part 2 (Table 2) L=2.25m -5

D = 0.033mm = 3.30 x 10 m

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Δx(avg)= 4.5cm = 4.5 x 10 m λ=?

Experimental Error: The experimental error cannot be exactly calculated since the actual wavelength of  the laser is a range between 640-660nm. However both calculations from the experiments are between this range, therefore it can be stated that out results were fairly accurate.

Why is this experiment so important in validating the wave theory of light?  This experiment undeniably proved that light travels in a wave and not only as a particle. Furthermore, it led to discussion as to why this really happens, which led to the d evelopment of empirical formulas allowing us to calculate different variables such as a light’s wavelength.

Sources of Error 

Variable wavelength of laser (640-660nm). The instability of the wavelength of the laser means the laser light is not perfectly coherent. As with incoherent light, the interference pattern would more broad, covering a larger spectrum of light. This means the nodal lines were not perfectly distinct, which would results to inaccuracy in our measurements.

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Inaccuracy in the measurement of the distance between the wall and the double slit grating. Since this measurement was conducted with a string and a meter stick, the accuracy of the distance would probably have not been very accurate. This would result in some inaccuracy in our final results, which is probably negligible.

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Inaccuracy in the actual marking of the nodal lines. As the light is projected on the screen, marking the exact position of the nodal lines cannot be fully accurate. Due to reasons such as the instability of holding the diffraction grating and relying our eyes to find the positions of the nodal lines.

Conclusion

The purpose of this lab was to determine the wavelength of a laser light using the technique observed in Young’s double slit experiment. By knowing the distance between the source of 

light and the screen, distance between nodal lines and spacing between each slits, we were able to calculate the wavelength of the light. The experiments proved to adequately successful

Labib Haque SPH4U

as our results fell in the wavelength range of the laser light. Possible error could have been caused by reasons stated in the “sources of error.” However the experiment proved to

successful meaning our method of conducting the experiment was good. This experiment can be improved by using a higher accuracy measuring instruments, perhaps a laser which can also calculate the distance between source and dot. Also, it can be possible to take a picture of the interference pattern and use a computer to more accurately find the distances between nodal lines.