3M Science at Home: Rainbow in a Jar experiment

Rainbow in a Jar

Key Concepts

  • Engineering Design icon.
    Engineering Design
  • Variables icon.

  • Introduction

    Have you ever looked at a straw in a glass, and it seems like it is in two separate pieces? Have you ever reached down to grab something underwater, and had to move your hand sideways to actually grab it? Both of those situations are examples of how water bends or refracts light. In this activity we will explore how refraction through water creates rainbows. 

  • Background

    Refraction, or the way light bends when it travels through different materials, was explained for the first time by a mathematician from Iraq named Ibn Sahl. He wrote a mathematical formula for how light bends through glass in the year 984 CE. He showed that you can predict how much light will bend when it passes through something that is not air. Since then, many more people have used this idea to calculate the speed of light through various materials. Isaac Newton did many experiments with prisms to try and learn how light and color were related, and further advanced scientific understanding of refraction.

  • Preparation

    Fill the jar about three-quarters of the way with water. 

  • Preparation

    1. Make a prediction. What will happen to the light as it passes through the water?
    2. Place the paper under the jar so that when light shines through the jar, you can see it on the paper.
    3. Let the sun shine directly on the jar, or shine your flashlight into the jar. Observe what you can see on the paper.
  • Observations and Results

    You should see a rainbow appear on the white paper. This is happening because different colors of light refract or bend at different angles through the water. White light, like from the sun or a flashlight bulb, is made up of a mix of all of the colors, which can be separated out using something like a prism, or a glass of water. The red light bends the least as it passes through the water, and violet light bends the most. That is why rainbows are always in order from red to violet. 

  • Clean Up

    Make sure to clean up when you are done. Pour the water down the drain, recycle the paper, and put the jar and flashlight back where they belong. 

  • More to Explore

    What if the light you are shining on the jar is not white light? Does that make a difference? Does an LED flashlight give different results than a flashlight with an incandescent bulb? How does what you learned with this experiment apply to other rainbows you may have seen? 

  • Safety First & Adult Supervision

    • Follow the experiment’s instructions carefully.
    • A responsible adult should assist with each experiment.
    • While science experiments at home are exciting ways to learn about science hands-on, please note that some may require participants to take extra safety precautions and/or make a mess.
    • Adults should handle or assist with potentially harmful materials or sharp objects.
    • Adult should review each experiment and determine what the appropriate age is for the student’s participation in each activity before conducting any experiment.

Next Generation Science Standard (NGSS) Supported - Disciplinary Core Ideas

This experiment was selected for Science at Home because it teaches NGSS Disciplinary Core Ideas, which have broad importance within or across multiple science or engineering disciplines.

Learn more about how this experiment is based in NGSS Disciplinary Core Ideas.

Disciplinary Core Ideas in Engineering Design & Physical Science

Physical Science (PS)4: Waves and Their Application in Technologies for Information Transfer

Grades 3-5

  • 4-PS4-1. Waves of the same type can differ in amplitude (height of the wave) and wavelength (spacing between wave peaks).

Grades 6-8

  • MS-PS4-1. A simple wave has a repeating pattern with a specific wavelength, frequency, and amplitude.

Grades 9-12

  • HS-PS4-1. The wavelength and frequency of a wave are related to one another by the speed of travel of the wave, which depends on the type of wave and the medium through which it is passing.

Grades K-2

  • 1-PS4-2. Objects can be seen only when light is available to illuminate them.
  • 1-PS4-3. Some materials allow light to pass through them.

Grades 3-5

  • 4-PS4-2. An object can be seen when light reflected from its surface enters the eye.

Grades 6-8

  • MS-PS4-2. When light shines on an object, it is reflected, absorbed, or transmitted through the object, depending on the object’s material and the frequency (color) of the light.
  • MS-PS4-2. The path that light travels can be traced as straight lines, except at surfaces between different transparent material (e.g., air and water, air and glass) where the light path bends.
  • MS-PS4-2. A wave model of light is useful for explaining brightness, color, and the frequency-dependent bending of light at a surface between media.