IB Physics SL C.3.7 Path difference

Practise using path and phase differences from source distances or ray diagrams to justify whether a point is a maximum or minimum.

Syllabus
First assessment 2025
Objective
—
Level
SL

Exam points

  • use source distances on a wave or ray diagram to calculate path difference and decide if a point is bright or dark
  • apply Δφ = 2πΔx/λ to convert a path difference into phase difference, keeping wavelength units consistent
  • show constructive or destructive interference by comparing Δx with nλ or (n + 1/2)λ on the diagram

C.3.7—Path difference question 1

[Maximum number: 1]

This question is about interference.

Light from a laser is incident on two identical parallel slits. The light from the two slits produces a fringe pattern on a screen.

Figure for Question C.3.7—Path difference question 1 — IB Physics SL

A central bright fringe is produced at C . The next bright fringe is produced at A . There is a dark fringe at B .

The distance from the two slits to the screen is 1.5 m . The distance BC is 1.8 mm and the distance between the slits is 0.30 mm .

State the path difference, in metres, between the waves that meet at B .

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