PH 122 Lecture Notes - Plane Wave, Diffraction
Document Summary
With wide barriers, the wave moves straight forward. With narrow openings, the wave spreads out behind the opening. Destructive interference occurs where a crest overlap a trough. An incident laser beam (a plane wave) shines on a screen with two slits. The two waves created overlap as they spread out behind the two slits. The two overlapped waves interfere, resulting in a pattern of light and dark bands on a screen. Constructive interference occurs with r1 and r2 differ by a whole number of wavelengths. Destructive interference occurs when r1 and r2 differ by a whole number of wavelengths plus half a wavelength. The bright fringes are labelled by the integer m, starting at the central maximum. As the number of slits in the grating increases, the fringes get narrower and brighter. M is the angle of the mth bright fringe. d is the distance between slits. ym = ltan m ym is the position of the mth bright fringe.