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What Happens When White Light Passes Through a Prism?

Published in Light Dispersion 3 mins read

When white light passes through a prism, it undergoes a fascinating optical phenomenon: the white light is separated into its component colors – red, orange, yellow, green, blue, and violet. This captivating display reveals that what we perceive as "white" light is, in fact, a combination of all the colors of the visible spectrum.

The Phenomenon of Dispersion

The separation of visible light into its different colors is precisely known as dispersion. This occurs because a prism is a transparent optical element with flat, polished surfaces that refract light. As white light enters the prism, each of its component colors bends at a slightly different angle.

Why Does Light Disperse?

The underlying reason for dispersion lies in how light interacts with the material of the prism:

  • Refraction: When light passes from one medium (like air) to another (like glass in a prism), it bends. This bending is called refraction.
  • Wavelength Dependence: Different colors of light have different wavelengths. For instance, red light has the longest wavelength in the visible spectrum, while violet light has the shortest.
  • Varying Refractive Index: The refractive index of a material is slightly different for each wavelength of light. This means that the prism's material causes shorter wavelengths (like violet) to bend more significantly than longer wavelengths (like red).

Consequently, as the light exits the prism, the colors spread out, creating a beautiful spectrum.

The Visible Light Spectrum

The spectrum produced by a prism displays the colors in a specific order, famously remembered by the acronym ROYGBIV:

  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Violet
Color Relative Refraction (Bending) Relative Wavelength
Red Least Longest
Orange
Yellow
Green
Blue
Violet Most Shortest

Historical Insights: Isaac Newton's Contribution

The understanding of light dispersion owes much to the groundbreaking work of Sir Isaac Newton in the 17th century. Through his famous experiments with prisms, he demonstrated conclusively that white light is not pure but rather a composite of various colors. He further proved that these separated colors could be recombined by a second prism to recreate white light, solidifying the concept of the visible spectrum.

Real-World Applications and Examples

The phenomenon of light dispersion through a prism isn't just a scientific curiosity; it has several real-world implications and natural occurrences:

  • Rainbows: Perhaps the most common natural example of dispersion, rainbows occur when sunlight passes through millions of tiny water droplets in the atmosphere, which act like tiny prisms, separating the light into its component colors.
  • Spectrometers: These scientific instruments use prisms (or diffraction gratings) to split light into its constituent wavelengths. Spectrometers are crucial in fields like chemistry and astronomy to analyze the composition of materials or distant stars.
  • Optical Devices: While lenses in cameras and eyeglasses aim to minimize dispersion (chromatic aberration), the principle is still understood and managed by combining different types of glass.

Understanding how white light separates into its vibrant components when passing through a prism reveals a fundamental aspect of light and its interaction with matter, shaping our perception of color and enabling various scientific advancements.