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Question: 

A thin film of oil $(n_o = 1.50)$ with varying thickness floats on water $(n_w = 1.33)$. When it is illuminated from above by white light, the reflected colors are as shown in Fig. 24–60. In air, the wavelength of yellow light is 580 nm.

  1. Why are there no reflected colors at point A?
  2. What is the oil’s thickness $t$ at point B?
Problem 48

Figure 24-60.

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

Quick Answer: 
  1. A half wavelength phase shift occurs due to reflection at the air-water interface, and oil thickness is so small that it doesn't add any significant phase shift.
  2. 290 nm

Giancoli 7th Edition, Chapter 24, Problem 48

(4:40)

Chapter 24, Problem 48 is solved.

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