Physics · Ch 10 — Wave Optics
Young's Double Slit Experiment
Young's Double Slit Experiment
In Young's arrangement, a narrow slit illuminated by a monochromatic source sends out a single expanding wavefront, which is allowed to fall symmetrically on two further narrow slits and , cut very close together (separation , typically a fraction of a millimetre) in an otherwise opaque screen placed just beyond . Because the same wavefront reaches and simultaneously (or with a fixed, constant lag), Huygens' principle applies to make and two secondary sources that are automatically coherent with each other, oscillating at the same frequency with a fixed phase relationship -- this is the division-of-wavefront method referred to in the previous section. …
What this figure shows. A schematic diagram in three vertical stages, left to right. On the far left, a single narrow slit S is shown illuminated by a monochromatic source, with curved wavefronts (arcs) expanding from S towards the right. These wavefronts strike an opaque screen with two narrow, closely spaced slits S1 and S2 (S1 above, S2 below, both at the same horizontal distance from S), the vertical separation between S1 and S2 labelled d. From S1 and S2, two more sets of expanding circular wavefronts (or straight lines representing rays) are drawn spreading rightward and overlapping in a shaded triangular overlap region between the slit-screen and a final vertical screen placed at horizontal distance D from the slits, with D drawn much larger than d. On this final screen, an alternating pattern of vertical bright (bright/white) and dark (shaded) bands is drawn, running parallel to the slits, symmetric about a labelled central point O directly opposite the midpoint of S1S2, with O itself marked as a bright fringe. A representative point P is marked on the screen above …