Light Dispersion Prism Simulator Guide

PhysicsIntermediateReading time: 3 min

Overview

In 1666, Newton let a beam of sunlight pass through a triangular prism in a dark room, and a beautiful ribbon of seven colors appeared on the wall. This experiment completely shattered the traditional belief that 'light is a pure, single entity'. This experiment takes you back to Newton's classic discovery, simulating the decomposition process of white light through a triangular prism to explore the minute differences in refractive properties of different monochromatic lights.

Background

Before Newton, it was widely believed that white light was the purest, and that colors were caused by some kind of 'pollution' of light by objects. Newton proved through the famous 'prism experiment' that white light is actually a mixture of lights of different colors. Even more ingeniously, he used a second prism to recombine the seven colors of light back into white light, indisputably confirming the theory of light dispersion. This discovery opened the door to spectroscopy, allowing us to even analyze the composition of stars billions of light-years away.

Key Concepts

Dispersion of Light

The phenomenon where polychromatic light decomposes into monochromatic lights. After white light passes through a prism, it decomposes into seven colors: red, orange, yellow, green, blue, indigo, and violet.

Spectrum

A band of colored light arranged in order of wavelength (or frequency) after polychromatic light is decomposed. It is the 'fingerprint' of white light.

Refractive Index and Frequency/Wavelength

n_{\text{violet}} > n_{\text{red}}

The refractive index of a medium is different for light of different colors. Light with higher frequency and shorter wavelength (such as violet light) has a larger refractive index and deviates more significantly.

Formulas & Derivation

Relationship between Deviation and Refractive Index

\delta \propto n - 1

Since the refractive index

n

of glass for violet light is larger, the angle of deviation

\delta

of violet light from its original propagation direction when passing through the prism is the largest, and red light is the smallest.

Experiment Steps

1
Recreate Newton's Experiment
Observe the process of a white light beam entering a triangular prism. What happens to the light at the first interface of the prism? Is the light beam still white after entering the prism?
2
Explore Deviation Angles
Drag the 'Incident Angle' slider to change the incident direction of the light. Carefully observe the colored light band leaving the prism. Which color of light deviates the most (absolute position is lowest)? Which deviates the least?
3
Compare Spectral Arrangement
Record the order of the seven colors: red, orange, yellow, green, blue, indigo, violet. Comparing their wavelength data, what pattern do you find between the refractive index and wavelength?
4
Explore Invisible Light
Click 'Show Infrared' and 'Show Ultraviolet'. In which regions of the spectrum are they located respectively? Based on this distribution, can you guess why infrared rays have a significant thermal effect?

Learning Outcomes

Confirm that white light is polychromatic light composed of seven monochromatic lights: red, orange, yellow, green, blue, indigo, and violet.
Master the order of the spectrum after dispersion and the difference in deviation ability it represents.
Understand the principle of prism dispersion: the same medium has different refractive indices for light of different wavelengths.
Recognize the invisible regions in the spectrum (infrared region and ultraviolet region).

Real-world Applications

Rainbow: Sunlight entering small water droplets in the air after rain undergoes refraction, reflection, and refraction again, resulting in dispersion phenomena.
Spectral Analysis: Scientists can determine the constituent elements of distant stars by analyzing the spectrum they emit.
Optical Fiber Communication: Using dispersion compensation technology to ensure signal integrity over long-distance transmission.
Gemstone Identification: The high dispersion value (fire) of diamonds is an important reason for their beauty and can also be used for authenticity determination.

Common Misconceptions

Misconception

The prism 'dyes' the light with color.

Correct

Incorrect. The prism simply 'sorts' the various monochromatic lights that already exist in white light through different refraction paths; it does not produce new colors.

Misconception

Infrared is red, and ultraviolet is violet.

Correct

Incorrect. Both infrared and ultraviolet are invisible to the naked eye. The red light we usually see from heaters is visible red light produced concomitantly, not the infrared itself.

Ready to start?

Now that you understand the basics, start the interactive experiment!

Start Experiment Start Quiz