how to make a rainbow science experiment

How To Make A Rainbow – Simple Science Experiments

Making a rainbow is a fun and educational science experiment that can be easily done at home or in the classroom.

It involves using a light source, such as sunlight or a flashlight, and a medium to separate the light into its component colors.

The result is a beautiful display of the colors of the rainbow, which can be used to teach about the nature of light and color.

This experiment is an engaging way to introduce children to the basics of optics and the physics of light.

How Are Rainbows Formed?

Sunlight or white light is a mixture of all the rainbow colors. The different rainbow colors are essentially mixed together to result in a white color.

You may wonder why when you mix all the different colors of paint together result in black instead of light. That is because light mixing is additive while pigment mixing is subtractive.

When light passes from one medium to another medium of a different density (e.g. from air to water ), the light bends. This is known as refraction of light ​1​  (More  light experiments ).

How much a light is refracted depends on the wavelength of the light. The shorter the wavelength, the more it bends. Because lights of different colors have different wavelengths , each color is refracted by different amounts.

Therefore, white light is split up after passing from air to water and the individual colors become visible. This dispersion of light allows us to see the spectrum of colors that form a rainbow ​2​ .

In nature, a rainbow is formed when sunlight is refracted on entering a droplet of water, reflected inside the back of the droplet and finally refracted again on leaving the droplet.

Seeing A Rainbow

To see a rainbow caused by sunlight, the sunlight needs to come from behind us because rainbows only appear in the part of the sky directly opposite the sun.

Red has the longest wavelength among the visible colors. So it tends to bend the least and the angle between the incident light and our line of sight for red is approximate 42 degrees. As a result, red appears on the top of the rainbow

Violet has the shortest wavelength. It tends to bend the most. To see violet, the angle between the incident light and our line of sight is roughly 40. So violet appears at the bottom of the rainbow.

Why Are Rainbows Arched?

Rainbows are not two dimensional . A rainbow is seen at an angle that is between 40-42 degrees from the incident sunlight . So all the water drops that produce each color in the rainbow lie on a three dimensional cone . Our eyes are at the tip of the cone.

That is why rainbows are arched. The circular shape below the ground is invisible.

Rainbow Experiment

Now are you ready to make some rainbows? Here are 3 easy ways to make your own rainbows at home. 

Warning: Adult supervision is vital in experiments involving sunlight. Do not look directly at the sun or at the reflection of sun in a mirror.

1. Rainbow Prism

One of the easiest and most visually stunning ways to see an artificial rainbow is by using a prism. Creating rainbows using a prism is really fun.

• strong sunlight
• glass prism
• white cardboard / paper (optional)
• adult supervision

Instructions

• Place a piece of white paper on the ground under the sunlight.
• Put the prism on or above the paper.

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2. Rainbow On The Wall

No prism? No problem. Using a small mirror and a glass, you can make a beautiful rainbow on the wall.

• a clear glass
• small mirror
• Fill the glass with water.

• Position the glass so that sunlight shines directly at the mirror. You may have to shift the mirror to find the right angle.
• Look for a reflection on the wall.  It would be easier to see if the room is dark.

3. Make A Rainbow Using Flashlight

You can still make a rainbow without natural light. Try this experiment using a whitelight flashlight.

• clear glass
• flashlight that emits strong focused white light . Flashlights that emit only yellowish light won’t work. Flashlights that don’t emit focused light also won’t work. Look for one with parabolic reflecting mirrors inside to focus the light, or one with a strong LED light.
• 2 pieces of white cardboard
• Cut a narrow rectangle in the middle of one piece of paper.

• Place the other piece of paper on the floor on the other side of the glass to catch the rainbow.

• Start from the glass and slowly move the flashlight farther and farther from the glass.

More Making a Rainbow Experiments

If you’re a rainbow enthusiast, want more rainbow experiments, or wonders what makes a rainbow, here are a few fun science projects for you.

• Rainbow Water
• Rainbow Walking Water
• Crystal Rainbow

Learn More About Rainbows

Have Fun With Rainbows

• 1. Jiang W, Chen RT, Lu X. Theory of light refraction at the surface of a photonic crystal. Phys Rev B . June 2005. doi: 10.1103/physrevb.71.245115
• 2. Whitaker RJ. Physics of the Rainbow. The Physics Teacher . May 1974:283-286. doi: 10.1119/1.2350374

Last update on 2024-12-18 / Affiliate links / Images from Amazon Product Advertising API

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How to Make a Rainbow

November 4, 2015 By Emma Vanstone 2 Comments

Did you know the light around us ( white light ) is actually made up of all the colours of the rainbow?

What are the colours of the rainbow?

Red, orange, yellow, green, blue, indigo and violet

Why do rainbows form?

Rainbows are seen in the sky opposite the sun and are caused by the refraction ( bending of light ) and dispersion ( splitting up ) of sunlight in drops of rain or mist. Sunlight hitting the rain or mist is dispersed into its constituent colours. This is because the light is reflected at varying angles, creating a rainbow as the different colours refract and bend by different amounts. Each colour of the rainbow has a different wavelength.

What is Refraction?

Refraction occurs when light bends as it passes through a transparent material, such as glass, prisms, or raindrops.

How to make a rainbow on a sunny day

Make a rainbow with a hosepipe.

If you have a spray bottle or hosepipe that can make a fine mist of water, you can make a rainbow on a sunny day.

Stand with your back to the sun and spray the hosepipe into the air. You might have to move it around to find the best angle for a rainbow.

Why can you see a rainbow through water?

Tiny drops of water act like a prism, splitting light into individual colours depending on their wavelength. Violet light is bent ( refracted ) the most and red the least.

The bending of light is called refraction , and the splitting of light into a rainbow of colours is called dispersion .

If you have a sunny day, you can also use a prism to make a rainbow.

Make a rainbow with a mirror

Try placing a mirror inside a glass and angling the glass so sunlight hits the mirror. You should be able to reflect a rainbow onto the wall.

Make a rainbow without the sun

Place a mirror inside a glass and shine a torch onto it until you can see a rainbow reflected onto the wall. You might have to adjust the angle of the glass to make it work.

If you can make a room very dark, you might also be able to see a rainbow by shining a torch through a prism.

Find Rainbows in Bubbles

When white light shines through the bubble film, it is reflected and dispersed, which splits the white light into its different wavelengths allowing you to see all the colours of the rainbow in the bubbles .

Rainbow Crafts for kids

Make rainbow paper like The Science Kiddo

We love this rainbow scavenger hunt from Hands On as We Grow .

Or how about a giant collage like The Imagination Tree?

Suitable for Key Stage 2 Science

If you enjoyed these activities don’t forget we have 100s more science experiments for you to try!

Last Updated on July 4, 2024 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Reader Interactions

November 05, 2015 at 4:50 am

Great. I once did that experiment, where i put mirror in the glass. Love that.

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• Activities for Kids

6 Incredibly Easy Rainbow Science Experiments

If you can’t find one, make one of your own, right in your kitchen, porch, or stoop

No rainbow in the sky today? No problem. Just pick one (or all) of these easy kid-friendly science experiments with your rainbow-making know-how. From reflection (mirror) to refraction (water glass) to learning about density, we’ve found six science experiments to make or learn from the rainbow. If you want more ideas, check out our sidewalk science ideas or dry ice science experiments .

1. The Mirror Method

Lesson: Demonstrate the principles of reflection and refraction with this easy experiment . Light bending, aka refraction, takes place as light waves pass through the water. When you shine your flashlight (or position your glass so the sun comes in) you are bending the light waves, each one of the waves at slightly different angles resulting in the different colors of the rainbow. This is the same basic principle that occurs when water and sunlight create a rainbow in the sky. Reflection is the light bouncing off of the mirrored surface.

You will need:

A small mirror (like a compact mirror)

A glass of water (big enough to hold the mirror)

A flashlight (or sunlight) 

A piece of white paper or a white wall

1. Put the mirror in the glass of water.

2. Turn off the lights and draw the curtains. Make sure the room is totally dark.

3. Shine the flashlight on the mirror and check out the cool mini-rainbows that appear above the mirror. Put your hand behind the glass for extra fun. 

2. The Garden Hose Technique

Lesson: Refraction, as above. This time, instead of using a mirror to reflect the light, you are going to basically mimic the natural formation of a rainbow by causing the water to hit the light in a fine mist.

A spray bottle or a hose

1. Put the hose on mist or grab your mister and spray it into an area of your yard/house/garden that has natural sunlight hitting it.

2. Let the kids ooh and ahh over your rainbow-making skills, then let each of them take a turn.

3. Water Density Rainbow

Lesson: By adding more or less sugar to each water solution you are creating different density levels. When you add coloring to the glasses you will be able to see which solution is the heaviest. Add the colors in rainbow order to impress the kids. Visit Little Bins for Little Hands for the experiment that shows you how to make a rainbow. 

Food coloring

Five glasses or plastic cups (clear)

4. The Glass o’ Water Approach

Lesson: The most simple form of light bending, this lesson in the light waves is similar to #1 above.

A glass of water

A piece of paper

1. Put the glass of water in the sunlight.

2. Put the paper next to it.

3. Let the sunlight stream through the water and create a rainbow on the paper.

5. Advanced Glass o’ Water Approach:

A spray bottle

1. Put the glass of water on a table or windowsill where there is sunlight.

2. Put the piece of paper on the floor where the sunlight hits, in the line of the glass.

3. Spray the window with warm water where the sun is coming through, and so it lines up with the paper. 

4. Move the glass and paper around until you see a neat little rainbow on the paper.

6. The Bubble Method

It doesn't get any easier than making a rainbow by blowing bubbles. You can use regular dish soap and a bit of water and shake ingredients inside a bottle, or just blow bubbles and observe. Want to up the fun factor? Make your own bubble mixture out of ordinary kitchen ingredients.

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Science Experiments

Rainbow in a Jar Science Experiment

Want to make your own rainbow? In this simple science experiment, kids can build their own rainbow in a jar while exploring density, mass, and volume.

Watch our demonstration video, gather your supplies, and print out our detailed instructions to get started. An easy to understand explanation of how it works is included below.

JUMP TO SECTION: Instructions | Video Tutorial | How it Works

Supplies Needed

• Tall Glass Jar
• Food Coloring: Red, Blue and Green
• 1/4 cup Honey
• 1/4 cup Blue Dish Soap
• 1/4 cup Water
• 1/4 cup Olive Oil
• 1/4 cup Rubbing Alcohol
• Jars for mixing and pouring
• Teaspoons for mixing

Rainbow in a Jar Science Lab Kit – Only $5

Use our easy Rainbow in a Jar Science Lab Kit to grab your students’ attention without the stress of planning!

It’s everything you need to  make science easy for teachers and fun for students  — using inexpensive materials you probably already have in your storage closet!

Rainbow in a Jar Science ExperimentInstructions

Step 1 – Add one drop of red food coloring and one drop of blue food coloring to 1/4 cup of honey and stir until combined. This creates a purple color liquid. Pour the purple liquid carefully into the tall jar.

Step 2 – Next add about 1/4 cup of blue dish soap to the tall jar.

Step 3 – Add a few drops of green food coloring to 1/4 cup of water and mix until combined. Then, carefully pour the green liquid into the tall jar. Tip: When pouring in the green liquid, tilt the jar so the liquid runs down the side of the jar slowly.

Step 4 – Wait a few moments and then slowly pour 1/4 cup of olive oil into the jar. Again, be very careful when pouring in the liquid. Make sure to tilt the jar and pour very slowly so the colors don’t mix.

Step 5 – Add a few drops of red food coloring to 1/4 cup of rubbing alcohol and mix until combined. Then, carefully pour the red liquid into the tall jar. Tip: I can’t stress enough how important it is to tilt the jar and pour slow. Otherwise, the colors will mix together and you won’t get a distinct rainbow.

Do you know why you were able to make the liquids form the rainbow in a jar? Find out the answer in the how does this experiment work section below.

Video Tutorial

How Does the Science Experiment Work

Density is the reason that this experiment works! Density is a measure of how much mass (or “stuff”) there is in a given volume. Density is a ratio of mass to volume and can be found by dividing an object’s mass by its volume (D=m/v).

Based on this equation, if the mass of something increases but the volume stays constant, then the density increases. Also, if mass decreases but the volume stays constant, then the density decreases. Density is all about how tightly packed the matter making up the material is in a given volume. Lighter liquids (like olive oil and rubbing alcohol) are less dense than heavier liquids (like honey and dish soap) because they have less matter in a given volume. Because olive oil and rubbing alcohol are less dense, they will float on top of liquids like water, dish soap, and honey. Liquids with a lower density will always float on top of liquids with a higher density.

All liquids have their own unique density. Water has a density of 1 g/mL (g/cm3). Objects will float in water if their density is less than 1 g/mL. Objects will sink in water if their density is greater than 1 g/mL.

I hope you enjoyed the experiment. Here are some printable instructions:

Instructions

• Add one drop of red food coloring and one drop of blue food coloring to 1/4 cup of honey and stir until combined. This is create a purple color liquid. Pour the purple liquid carefully into the tall jar.
• Next add about 1/4 cup of blue dish soap to the tall jar.
• Then add a few drops of green food coloring to 1/4 cup of water and mix until combined. Then carefully pour the green liquid into the tall jar. Tip: When pouring in the green liquid, tilt the jar so the liquid runs down the side of the jar slowly.
• Wait a few moments and then slowly pour 1/4 cup of olive oil into the jar. Tip: Again, be very careful when pouring in the liquid. Make sure to tilt the jar and pour very slowly so the colors don’t mix.
• Add a few drops of red food coloring to 1/4 cup of rubbing alcohol and mix until combined. Then carefully pour the red liquid into the tall jar. Tip: I can’t stress enough how important it is to tilt the jar and pour slow. Otherwise the colors will mix together and you won’t get a distinct rainbow.

Reader Interactions

October 15, 2017 at 3:22 pm

It was cool. Was it density

October 30, 2017 at 11:33 am

Hi it was Cooooolllllll….. It was because of the density

June 12, 2018 at 10:22 am

my kids enjoyed this presentation. They are doing it for a stem project

March 25, 2019 at 3:41 pm

How long did this project take to make and how long did it last until the colors started to mix? Also, what would be the guiding question of an experiment like this?

March 2, 2023 at 11:46 am

1.This experiment took around 20 minutes to put together. 2. It lasts for as long as you need if nobody touches it. 3. A leading question to this experiment could be ” Will all of the ingredients mix while i am pouring?”

I hope this helped:)

January 23, 2020 at 12:41 pm

its amazing my students loved it!

March 2, 2023 at 11:40 am

I did this exact project for the science fair this year and I won 2nd place. I made a full board about destiny and I made a question saying ” If I do not tip the jar or if i pour too fast, will the colors mix? The answer is yes! The colors did mix whenever I didn’t tip the jar and the rubbing alcohol sank down and mixed with the green and then since the extra liquid was in the green it mixed with the blue dish soap and began to be a big bubbly mess! 🙂

June 12, 2023 at 10:15 am

Can you put a top on the jar, shake the jar, mixing the liquids, will the liquids separate after sitting for hours or days?

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