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.
Predict before you look
- Fringe spacing is Δy = λL/d. Which of those three quantities sits in the denominator?
- A bright fringe occurs where the path difference is a whole number of wavelengths. What does that make the path difference at the central fringe?
Nothing to submit here — these are to think through, so the prediction below is an informed one rather than a guess.
Commit to an answer now. It is not graded and being wrong costs nothing — the point is to have something specific to reconcile against once you have the data.
Answer every prediction to unlock the lab. A sentence is enough.
Run the investigation
Predictions first
The procedure and the simulation unlock once you have committed above. Observing before predicting is how a wrong intuition survives a lab intact.
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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