Thin Film Interference Pattern

Colours are often observed when gasoline is poured onto water. This effect is primarily produced by

• diffraction

• diffuse reflection

• interference

• absorption

• incandescence

Figure 2 shows three experiments for studying the interaction of monochromatic light with thin films of glass of various thickness t. The eye represents the position of the observer. The observer sees constructive interference in

• I only

• II only

• III only

• I and III only

• II and III only

A thin coating, of refractive index 1.2, is applied to a glass camera lens, of refractive index n > 1.2, to minimize the intensity of the light reflected. The wavelength of the light is . The coating thickness required to minimize the intensity of reflected light is

The thickness of a human hair is to be measured using the interference pattern produced by an air wedge. Red light with a wavelength of 638 nm is used on an air wedge that is 25.0 cm long. If 10 bright fringes are counted across 1.06 cm in the air wedge, what is the thickness of the hair?

• 752 µm

• 576 µm

• 75.2 µm

• 57.6 µm

• 780 µm

A construction company designs a new office tower with an outer surface mostly made of glass (nglass = 1.52). The company wishes that the glass appear a reddish-orange without having to use coloured glass. Instead, a thin film (nfilm = 1.65) is used that maximizes the reflection of that colour of light (wavelength 615 nm). What thickness would this film need to be?

• 1.5 x 10-8 m

• 2.67 x 10-8 m

•  8.67 x 10-8 m

•  1.2 mm

• 9.32 x 10-8 m

The interference pattern created by monochromatic light in an air wedge is used to measure the thickness of an object. Which of the following changes would cause the spacing between adjacent fringes to increase?

• Use a light source with a higher frequency.

• Increase the thickness of the object being measured.

• Use a light source with a longer wavelength.

• Use a shorter air wedge.