26_InstSolManual_PDF_Part5

# Set up the fringes are produced by interference

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Set Up: The fringes are produced by interference between light reflected from the top and from the bottom surfaces of the air wedge. The refractive index of glass is greater than that of air, so the waves reflected from the top surface of the air wedge have no reflection phase shift and the waves reflected from the bottom surface of the air wedge do have a half-cycle reflection phase shift. The condition for constructive interference (bright fringes) therefore is The geometry of the air wedge is sketched in Figure 26.21. Figure 26.21 Solve: so and The distance along the plate between adjacent fringes is The number of fringes per cm is Reflect: As the interference is destructive and there is a dark fringe at the line of contact between the two plates. t S 0 1.00 D x 5 1.00 0.0369 cm 5 27.1 fringes / cm. D x 5 x m 1 1 2 x m 5 l 2 1 8.89 3 10 2 4 2 5 656 3 10 2 9 m 2 1 8.89 3 10 2 4 2 5 3.69 3 10 2 4 m 5 0.369 mm. x m 1 1 5 A m 1 3 2 B l 2 1 8.89 3 10 2 4 2 . x m 5 A m 1 1 2 B l 2 1 8.89 3 10 2 4 2 t m 5 A m 1 1 2 B l 2 . t 5 1 8.89 3 10 2 4 2 x . tan u 5 t x tan u 5 0.0800 mm 90.0 mm 5 8.89 3 10 2 4 . u x 9.00cm t 0.0800mm Air 2 t 5 A m 1 1 2 B l . 2 t l 5 17.52 3 10 2 6 m 480 3 10 2 9 m 5 36.5. l 5 648 nm 1.35 5 480 nm. l 5 l 0 n . 2 t 5 17.52 3 10 2 6 m. t 5 l / 4 n . t 5 l / 2 n . m 5 2, t 5 m 1 505 nm 2 3 2.62 4 2 5 1 96.4 nm 2 m . 2 t 5 m l . 180° l 5 505 nm 2.62 . 180° 1 n 5 1.62 2 1 n 5 2.62 2 180° 1 n 5 2.62 2 1 n 5 1.00 2 Interference and Diffraction 26-5

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