An air wedge is formed between two glass plates separated at one edge by a very

Question

An air wedge is formed between two glass plates separated at one edge by a very fine wire of circular cross section as shown in Figure P37.35. When the wedge is illuminated from above by 500-nm light and viewed from above, 25 dark fringes are observed. Calculate the diameter d of the wire.

An air wedge is formed between two glass plates separated at one edge by a very fine wire of circular cross section as shown in Figure P37.35. When the wedge is illuminated from above by 500-nm light and viewed from above, 25 dark fringes are observed. Calculate the diameter d of the wire.

Explanation / Answer

2t = m(lambda)

For 25 dark fringes, including the one where the plates meet:

t = [24(500 x 10^ -9 m) ]/ 2

t = 6 x 10^-6 m

Thus, the diameter of the wire is:

r = t /2

r = (6.6 um /2) = 3.3 um

d = 2r = 2(3.3 um) = 6.6 um [ANS]

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