CK-12-Physics-Concepts - Intermediate

15.1. Double Slit Interference http://www.ck12.org

λ=xdL

Example Problem:Monochromatic light falls on two narrow slits that are 0.0190 mm apart. A first order fringe is
21.1 mm from the central line. The screen (back wall) is 0.600 m from the slits. What is the wavelength of the light?

Solution:λ=xdL =(^0.^021 (m 0 .)( 6000.^000019 m) m)= 6. 68 × 10 −^7 m

Summary

• The last particle of medium at the back corner of an impenetrable barrier will act as a point source and produce
  circular waves.


• Diffraction is the bending of waves around a corner.


• Constructive interference occurs when two wave crests overlap, doubling the wave amplitude at that location.


• Destructive interference occurs when a wave crest overlaps with a trough, causing them to cancel out.


• Light is a wave, and creates an interference pattern in the double slit experiment.


• An interference pattern consists of alternating bright and dark lines; the bright lines are called fringes.


• In a double slit experiment, the wavelength can be calculated using this equation: λ=xdL

Practice

Questions

http://www.youtube.com/watch?v=AMBcgVlamoU

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/75711

Follow up questions:

1. When the amplitude of waves add, it is called _____ interference.


2. When the amplitude of waves subtract, it is called _____ interference.


3. What do we call the phenomenon of light bending around a corner?

Review

Questions

1. Destructive interference in waves occurs when
   (a) two troughs overlap.
   (b) crests and troughs align.
   (c) two crests overlap.
   (d) a crest and a trough overlap.


2. Bright bands in interference patterns result from
   (a) destructive diffraction.
   (b) destructive interference.
   (c) constructive diffraction.