IB Physics SL C.3.8 Two-Source Interference

Practise using path difference and phase to locate constructive or destructive interference and calculating fringe separation for coherent light, sound or water-wave sources.

Syllabus
First assessment 2025
Objective
—
Level
SL

Exam points

  • set path difference to mλ for constructive interference and (m + ½)λ for destructive interference
  • convert path difference to phase difference with 2πΔx/λ before classifying the point
  • apply fringe spacing λD/d with slit separation and screen distance in consistent units

C.3.8—Two-source interference 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.3.8—Two-source interference 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 .

State the phase difference between the light waves from the two slits that meet at B .

All question bank results loaded