Thin film interference

Definition

Thin film interference occurs when light waves reflected off the upper and lower boundaries of a thin film interfere with one another, creating constructive or destructive interference. This phenomenon is responsible for the colorful patterns seen in soap bubbles and oil slicks.

5 Must Know Facts For Your Next Test

1. Constructive interference occurs when the path difference between two reflected waves is an integer multiple of the wavelength.
2. Destructive interference happens when the path difference is an odd multiple of half-wavelengths.
3. The thickness of the film and the wavelength of light determine whether the interference will be constructive or destructive.
4. A phase shift of $\pi$ (half a wavelength) can occur upon reflection from a medium with a higher refractive index.
5. Thin film interference can be observed in everyday phenomena like soap bubbles, oil films on water, and anti-reflective coatings.

Review Questions

• What conditions must be met for constructive interference to occur in thin film interference?
• How does the phase shift affect thin film interference patterns?
• In what everyday objects might you observe thin film interference?

Related terms

Constructive Interference:

Occurs when two or more waves combine to produce a wave with greater amplitude.

Destructive Interference:

Occurs when two or more waves combine to produce a wave with lower amplitude.

Phase Shift:

A change in phase of a wave, often occurring upon reflection from a medium with different optical properties.