A simple science demonstration can transform ordinary household items into a brilliant display of color. Creating a rainbow effect indoors or out offers a hands-on way to explore the nature of light. This accessible experiment is easy to set up and engaging for observers of all ages. The process relies on manipulating a beam of light to reveal the hidden components that make up what we perceive as white light.
Materials for the Indoor Rainbow
To perform the indoor experiment, gather a few simple items that mimic the atmospheric conditions producing natural rainbows. You will need a small, clear glass or bowl that holds water, and a handheld mirror small enough to fit inside the container. You also need a source of bright, focused white light, such as direct sunlight or a powerful flashlight. Finally, a piece of white paper or a white wall is necessary to act as a screen to catch and display the resulting spectrum.
Step-by-Step Instructions for Creating the Spectrum
Begin by filling the clear glass or bowl almost full with water. Carefully place the small mirror into the water at a slight angle, resting it against the inside edge of the container. Position the glass near a window so direct sunlight hits the submerged mirror.
If sunlight is unavailable, darken the room and shine a bright flashlight directly at the submerged mirror. Hold the white paper or position the white wall to catch the reflected light. Slowly adjust the angle of the mirror or the paper until a clear band of colors—red, orange, yellow, green, blue, and violet—becomes visible.
The Physics of Light Dispersion
Refraction and Dispersion
The appearance of the multicolored arc results from two optical phenomena: refraction and dispersion. White light is a mixture of all colors of the visible spectrum, each corresponding to a different wavelength. When light travels from air into a denser medium, such as water, it slows down and changes direction—a process known as refraction.
Wavelength Separation
Each wavelength travels at a slightly different speed within the water, causing the amount of refraction to vary by color. Shorter wavelengths, like violet and blue light, bend more than longer wavelengths, like red and orange light. This separation of white light into its constituent colors is called dispersion. The water and glass structure function similarly to a prism, bending and splitting the light before the mirror reflects the separated colors onto the screen.
Quick Outdoor Rainbow Methods
Creating a rainbow effect outdoors mimics the natural process of light passing through atmospheric water droplets. Position yourself with the sun directly behind you, ensuring your shadow is cast forward, as the rainbow is viewed at a fixed angle relative to the sun and the water source. The simplest method uses a garden hose equipped with a nozzle that produces a fine mist. Spray the water forward and slightly upward, aiming toward the area in front of your shadow, and slowly adjust the angle until sunlight hits the fine curtain of water droplets. Alternatively, a spray bottle set to its finest mist setting can create a smaller, handheld rainbow, where the droplets act as millions of tiny prisms refracting and dispersing the sunlight.