PhysicsRankPREVIEWTry a problem

THE PRACTICE STUDIO

Go slowly. Ask why. Make it yours.

PRACTICE · MEMBERSIntermediate · Single correct

PRACTICE / Thin-film interference

Turn fringe spacing into a physical gap

A straight air wedge is 30 mm long from contact to its raised edge. Under 600 nm near-normal illumination, successive reflected dark fringes are 0.75 mm apart.

What is the gap thickness at the raised edge?

Organize the givens & assumptions
  • Wedge length = 30 mm
  • Fringe spacing = 0.75 mm
  • λ₀ = 600 nm

Coherent monochromatic light, lossless ordinary dielectric interfaces, normal or explicitly stated incidence, and the two principal reflected beams. Higher reflections are neglected unless stated; phase extrema do not imply exact zero reflectance.

  1. A6 μm6\ \mu\mathrm m
  2. B0.30 μm0.30\ \mu\mathrm m
  3. C12 μm12\ \mu\mathrm m
  4. D24 μm24\ \mu\mathrm m

Try it on paper first. Free sample problems in every collection include the complete reasoning: find one in this collection →