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title: "Coherent monochromatic light of wavelength \\(\\lambda\\) passes through two narrow slits, \\(S_1\\) and \\(S_2\\), separated by a distance \\(d\\), and illuminates a distant screen. Point \\(P\\) is the location of the first dark fringe (first interference minimum) above the central bright maximum. Which of the following diagrams best represents the path length difference \\(\\Delta L\\) and the spatial phase relationship of the two waves as they arrive at point \\(P\\)?"
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url: "https://nerd-notes.com/ubq/123356/"
date_modified: "2026-09-28T11:58:14+00:00"
---

# Coherent monochromatic light of wavelength \(\lambda\) passes through two narrow slits, \(S_1\) and \(S_2\), separated by a distance \(d\), and illuminates a distant screen. Point \(P\) is the location of the first dark fringe (first interference minimum) above the central bright maximum. Which of the following diagrams best represents the path length difference \(\Delta L\) and the spatial phase relationship of the two waves as they arrive at point \(P\)?

Coherent monochromatic light of wavelength \(\lambda\) passes through two narrow slits, \(S_1\) and \(S_2\), separated by a distance \(d\), and illuminates a distant screen. Point \(P\) is the location of the first dark fringe (first interference minimum) above the central bright maximum. Which of the following diagrams best represents the path length difference \(\Delta L\) and the spatial phase relationship of the two waves as they arrive at point \(P\)?

- **A.** Diagram A: Path difference \(\Delta L = \lambda\) with wave crests aligned at point \(P\)
- **B.** Diagram B: Path difference \(\Delta L = \dfrac{1}{2}\lambda\) with wave crests aligned at point \(P\)
- **C.** Diagram C: Path difference \(\Delta L = \dfrac{1}{2}\lambda\) with a wave crest and a wave trough meeting at point \(P\)
- **D.** Diagram D: Path difference \(\Delta L = \dfrac{1}{4}\lambda\) with a wave crest meeting a zero-crossing node at point \(P\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123356/*