Chapter 35&36 Interference and the Wave Nature of Light 1.Light as a Wave 2.THE PRINCIPLE OF LINEAR SUPERPOSITION 3.Young's Double-Slit Experiment 4.Diffraction

What is physics?

Light as a Wave Huygens' principle: All points on a wavefront serve as point sources of spherical secondary wavelets. After a time t, the new position of the wavefront will be that of a surface tangent to these secondary wavelets.

Constructive Interference Condition :, m=0, 1, 2, 3, ….

Destructive Interference Condition:, m=0, 1, 2, 3, ….

Young's Double-Slit Experiment

Bright fringes: Dark fringes: Where m=1, 2, 3, ∙∙∙

Example 1 Young’s Double-Slit Experiment Red light (λ=664 nm in vacuum) is used in Young’s experiment with the slits separated by a distance d=1.20×10 –4 m. The screen in Figure is located at a distance of L=2.75 m from the slits. Find the distance y on the screen between the central bright fringe and the third- order bright fringe.

Interference from Thin Films Condition for destructive interference is:

Diffraction The diffraction is the bending of waves around obstacles or the edges of an opening

Diffraction determined by the ratio λ /W Smaller λ /W, less diffraction Larger λ /W, more diffraction

Conditions for dark fringes Conditions for dark fringes in single-slit diffraction:

Example Single-Slit Diffraction Light passes through a slit and shines on a flat screen that is located L=0.40 m away (see Figure). The width of the slit is W=4.0×10 –6 m. The distance between the middle of the central bright fringe and the first dark fringe is y. Determine the width 2y of the central bright fringe when the wavelength of the light in a vacuum is (a) λ=690 nm (red) and (b) λ=410 nm (violet).