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Young's Slits - Page 7 of 8

If you have come in at this page, please go to the Young's Slits Introduction to read the introductory information. There operating instructions are on page 6.

Live Interactive Experiment

IMPORTANT NOTE: This is a real live experiment that you can control. This is not a simulation. Click controls slowly and wait for a response. There may be a delay depending upon the overall speed of the link. Also note that the count rate (CPS) only updates approximately every five seconds. This is because the microcontroller counts photons for five seconds.

Common Problems:

Problem Probable Causes Solutions
No applet displayed Java not installed Install Java. Java enables programs to run in your browser in a safe and secure manner.
Java installed but no applet Security settings Open Java console and look for errors
Gate indicator static Experiment down Notify Teralab
Unable to control experiment Experiment in use Watch or try back later
Not in use but no response Not in control Click 'Take Control'
Count rate is zero Discriminator level too high Set discriminator to 12dB
Count rate never increases above 30CPS Both lasers are off Click on a laser to turn it on
No interference fringes Using a single slit mask Use masks 1 to 4

Graph Template:

For a graph template for the results in Excel format, right click on the icon and choose 'Save Target As...'. Chose the appropriate worksheet tab for the type of results that you want to plot. Complete the boxes that are highlighted in yellow. If you need to change the scale, double click on the Y axis and select the Scale tab. This spreadsheet can be used with OpenOffice.

Mask Specifications:

Mask No. of Slits Slit Width Slit Separation (a)
1 2 0.08mm 0.25mm
2 2 0.04mm 0.25mm
3 2 0.08mm 0.125mm
4 2 0.04mm ?
5 1 0.08mm N/A
6 1 0.04mm N/A

Figures and Formulae:

Typical discriminator level setting 12dB.
Blue laser wavelength 405nm
Red laser wavelength is longer than the blue.
Acceptance slit step 0.265mm.
Acceptance slit width 0.2mm.
Counter / timer gate 5 sec.
y = λD / a
y = distance between fringes (m).
λ = wavelength (m).
D = distance from slits mask to acceptance slit (0.57m).
a = distance between slits (m).

Report Faults

If you experience problems, there may be a fault or a software bug I don't know about. Please email details of the problem to and I will look into it.

Answers and References

The 'missing values' and a summary are given on the next page, along with some references for further study.

Page Title Description
Background Introduction to diffraction and Young's slits.
Information Encoding This page attempts to show the similarities between the frequency content of an electrical waveform and the diffraction pattern of an object.
Project Construction Information about how the experiment was built.
Single Photon Justification Mathematical justification that the experiment can be considered to be diffracting individual photons.
Quiz A multiple choice quiz (requires Java).
Instructions Instructions for operation of the experiment.
Conclusion Conclusion and references.

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