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Question: 

A fine metal foil separates one end of two pieces of optically flat glass, as in Fig. 24–33. When light of wavelength 670 nm is incident normally, 24 dark bands are observed (with one at each end). How thick is the foil?

(a) Light rays reflected from the upper and lower surfaces of a thin wedge of air (between two glass plates) interfere to produce bright and dark bands.

Figure 24-33 (a) Light rays reflected from the upper and lower surfaces of a thin wedge of air (between two glass plates) interfere to produce bright and dark bands.

(b) Pattern observed when glass plates are optically flat;

Figure 24-33 (b) Pattern observed when glass plates are optically flat;

(c) pattern when plates are not so flat. See Example 24–10.

Figure 24-33 (c) pattern when plates are not so flat. See Example 24–10.

Source: Giancoli, Douglas C., Physics: Principles with Applications, 7th Edition, 2014.

Quick Answer: 

$7.7 \; \mu m$

Giancoli 7th Edition, Chapter 24, Problem 52

(2:46)

Chapter 24, Problem 52 is solved.

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