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Difficulty: MediumPhysics Fundamentals and Everyday Applications

When a thin film of oil floating on water is exposed to white sunlight, vibrant multicolored bands are observed across its surface. Which physical phenomenon is primarily responsible for the formation of these colors?

  1. A
    Total internal reflection of light rays trapped entirely inside the oil layer
  2. Interference between light waves reflecting from the upper and lower surfaces of the oil filmAnswer
  3. C
    Rayleigh scattering of shorter wavelengths by suspended oil particles
  4. D
    Refraction and angular dispersion of white light as it passes through oil droplets acting as miniature prisms

Answer

Interference between light waves reflecting from the upper and lower surfaces of the oil film
The brilliant colors seen on an oil slick or soap bubble are caused by thin-film interference. When white light falls on the film, a portion reflects from the top surface and another portion reflects from the lower surface. Because the light reflecting from the bottom surface travels a slightly longer path through the oil, the two reflected light waves superimpose. Depending on the film's thickness and the wavelength of light, certain colors interfere constructively (appearing bright) while others interfere destructively, generating bright color patterns.

Step-by-Step Solution

1
Identify the optical boundary interaction
Sunlight striking the thin oil layer on water encounters two interfaces: the air-oil top interface and the oil-water bottom interface.
Light is partially reflected at the top boundary and partially transmitted into the oil layer before reflecting off the bottom boundary.
2
Analyze the phase shift and path difference
The wave reflecting from the bottom interface travels an extra distance equal to twice the thickness of the film.
The optical path difference between the two reflected rays determines whether specific colors undergo constructive or destructive interference.
3
Determine the cause of the observed color spectrum
Varying thickness across the oil film leads to constructive interference of different spectral colors at different locations, creating brilliant multicolored bands.
This behavior is a classic manifestation of thin-film wave interference.

Key Concept

Thin-film interference of light waves
Estimated Time:1m 0s
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Topics

Physics Fundamentals and Everyday Applications

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