Why are fringes are formed in the Young double slit experiment?

In the Young double slit experiment, coherent light of wavelength λ from a single source illuminates a system of two slits separated from each other by a small distance a. Each slit causes the light entering it to diffract, and behaves like a light source. Light from each slit is then observed on a screen at a distance D far away from the set of slits.At certain points on the screen, the light waves from each slit arrive in phase (phase difference of 2nπ, with n an integer) with each other, due to the difference in the length the waves have travelled (path difference) being nλ. This causes constructive interference and produces a bright fringe. At other points, the waves from each slit arrive in anti-phase (phase difference of (2n+1)π), corresponding to a path length of (2n+1)λ/2, causing destructive interference and producing no resultant wave which looks like a dark fringe. As a result, an alternating pattern of light and dark fringes is formed. The spacing Δx between light fringes is found using Δx = Dλ/a.

JP
Answered by Joe P. Physics tutor

10656 Views

See similar Physics A Level tutors

Related Physics A Level answers

All answers ▸

Compare and contrast geostationary and low polar orbits.


What is EMF? How do we test for it?


A body is moving at 70km/h and has a mass of 130kg, calculate its maximum kinetic energy.


A uniform plank of wood of mass 32 kg and length 4.0 m is used to cross a ditch. In the ditch is a rock, which is used to support the plank horizontally 0.80 m from one end. The other end is supported by the bank. Calculate the rock's supporting force.


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning