13_Chapter 24 HomeworkCH24 Wave Optics

13_Chapter 24 HomeworkCH24 Wave Optics - Wave Optics 24.22...

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Unformatted text preview: Wave Optics 24.22 315 Light reflecting from the lower surface of the air layer experiences phase reversal, but light reflecting from the upper surface of the layer does not. The requirement for a dark fringe (destructive interference) is then λ 2 t = mλn = m = m λ , where m = 0 , 1, 2,… nair At the thickest part of the film ( t = 2.00 µ m ) , the order number is m= 2t λ = 2 ( 2 .00 × 10 −6 m ) 546.1 × 10 −9 m = 7.32 Since m must be an integer, m = 7 is the order of the last dark fringe seen. Counting the m = 0 order along the edge of contact, a total of 8 dark fringes will be seen. 24.23 With a phase reversal upon reflection from the lower surface of the air layer and no phase change for reflection at the upper surface of the layer, the condition for destructive interference is λ 2 t = mλn = m = m λ , where m = 0 , 1, 2,… nair Counting the zeroth order along the edge of contact, the order number of the thirtieth dark fringe observed is m = 29 . The thickness of the air layer at this point is t = 2r , where r is the radius of the wire. Thus, −9 t 29 λ 29 ( 600 × 10 m ) = = 4.35 µ m r= = 2 4 4 Incident light n t3 t2 t1 O ...
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This document was uploaded on 10/20/2011.

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