Explain how wavelength, distance, and slit spacing set fringe spacing
Three steps, the way the exam actually works: work through the lab, write down your own observations, then answer a 6-point free response. What you recorded goes to the grader with your writing, so a conclusion that does not follow from your own evidence will cost you the point — exactly as it would with a real reader.
Run the investigation
- 1Run the wave lab with two sources and observe the bright and dark interference lines.
- 2Increase the wavelength and record how the fringe spacing changes.
- 3Increase the screen distance and record how the fringe spacing changes.
- 4Increase the source separation and record how the fringe spacing changes.
Booting the lab…
Record what you found
This is your reading of the source, not ours. The grader sees them, so your conclusions have to follow from what you actually recorded.
| Effect of increasing wavelength | |
|---|---|
| Effect of increasing screen distance | |
| Effect of increasing source separation | |
| Fringe-spacing relationship you infer |
Answer the free response
The interference pattern changes in systematic ways. (a) State the relationship among fringe spacing, wavelength, screen distance, and slit separation, and explain which variables increase or decrease the spacing. (b) Use path difference to explain why bright fringes and dark fringes alternate. (c) Explain why the central maximum sits on the symmetry line. (d) A student doubles both wavelength and slit separation and predicts the fringes will spread out because the wavelength got larger. Evaluate the prediction quantitatively.
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