PhysicsLAB Practice Problems
Thin Film Interference Soap Bubbles

Directions: On this worksheet you will be investigating the basic properties of thin film interference.



Question 1  A thin soap bubble, n = 1.35, is filled with air. Since the medium outside the bubble is also air, at which of the interfaces (air-soap and soap-air) would the light undergo a 180° phase change upon reflection?
Question 2  What is the wavelength of red, 639-nm light as it travels through the film?
Question 3  At what minimum non-zero thickness of the film will the intensity of the red light reflected back into the air be a maximum?
Question 4  At what minimum non-zero thickness of the film will the intensity of the same red light reflected back into the air be a minimum, or experience destructive interference?
Question 5  In general, when red light is removed from white light, the soap bubble would appear to be which color?
Question 6  What is the frequency of the red light as it travels through the soap film?
Question 7  If the soap film were instead specified to be 598 nanometers thick, which wavelength in the visible spectrum would be canceled?


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