How to Use a Magnifying Glass to Start a Fire: STEM Experiments

Last Update: May 25th, 2022

Reviewed & Fact Checked by Lori Stutts

Before moving forward, it’s very important to note that this experiment will require adult supervision as it will involve heat that may cause harm to both adults and children.

This experiment has been a subject of cartoon humor and TV show and movie references for decades. From the world-renowned Bugs Bunny to many other pop culture icons, the Magnifying Glass experiment has been a fascinating enigma to children the world over.

It’s a truly charming and easy-to-do experiment that can entertain children as they explore the great outdoors. It must be noted, however, that this experiment will involve heat that can reach unsafe levels so utmost care is required.

The Experiment

That said, the experiment is very flexible and entertaining to execute. With adult supervision, you and the kids can test a variety of variables for this experiment such as timing the total time it takes before certain materials start burning, layering dried leaves to see how long it takes for the sunbeam to burn through the materials, and many more. The science behind this phenomenon leaves much to the imagination for the execution.

To run this experiment, here are the things you can consider gathering for this experiment:

  • Magnifying Glass
  • Dried Leaves
  • Paper
  • Source of water such as a water bottle to put out the fire quickly if needed 
  • Other materials you wish to try the experiment on

Now, admittedly, certain weather conditions have to be set in order to achieve the best results for this experiment. The more sunlight you have in the backyard, the more effective the sun rays will become.

You can also add an element of artistry to this project by drawing images that you can trace using your magnifying glass laser ray. When you have the magnifying glass at hand, you’re ready to hit the outdoors with the kids. 

The next step is to locate and pinpoint a safe location for the activity. Take a place where the fire cannot spread hastily to anything else into consideration as there will be a need to execute the activity outdoors because a flame is to be created using a magnifying glass.

To start the experiment, lay the leaves down or hold them up for the kids. Make sure the adults carefully supervise this juncture as this is the most sensitive aspect of the project. Hold the magnifying glass between the paper and the sun.

When you position the magnifying glass between the sun and the material you apply the experiment on, you will notice that there will be concentrated sunrays on the surface of the paper or leaves.

By manipulating the proximity of the paper and the magnifying glass itself, you will notice that the dot of the concentrated paper can be made smaller or bigger. Do note, though, that the bigger this dot is, the longer it will take for the surface to burn as the sun rays are less concentrated.

Burn through the materials you have on hand and perform the experiments that pique your and the kid’s interests and curiosities. If you and your children draw shapes on paper, feel free to trace them using the beam of light. You can also manipulate variables such as materials used for the experiment, or even the proximity of the magnifying glass to each of the materials. It would also be entertaining to see what materials take the longest to burn.

You can also try putting a water droplet on the lens. This will intensify the sunlight’s heat that can cause the fire to ignite quickly. Try comparing the results between a magnifying glass with a droplet and one without.

It might also be entertaining to use larger lenses, as this makes it even easier to create a fire on any flammable material. You may compare the results with smaller magnifying glasses or those with droplets on lenses.

Ask the kids to focus the dot on a certain place for a few seconds or minutes so they can experience it for themselves. As time wears on, you will notice that smoke will slowly emerge from the focused areas before a fire finally starts burning.

Once the kids finish playing, make sure that all fires made are accounted for and put out.

The Science Behind the Activity

This seemingly magical exhibition is charming as it is entertaining. But what science is at work here? What properties and characteristics of matter took over to make this experiment possible?

The activity highly relies on the unique properties of the magnifying glass in this magic trick that conjures fire by harnessing the power of the sun.

It is no secret that the main purpose of the magnifying glass is to make everything appear bigger than it actually looks. Creating the fire that you did through this experiment can be explained through the behavior of photons. Photons are subatomic particles that carry or hold the clear visible light of the sun as it moves towards the earth. These particles transmit light and energy in the form of heat.

To set fire to things, the magnifying glass focuses all the photons into a small area or the dot that you see throughout the experiment. This area is where the magnifying glass diverts the photons that carry heat and light energy. It diverts these photons through its convex lens, a special shape for glass curved outwards.

When the sunlight falls through the magnifying glass, the appropriate focal strength of the photons moves through the lens to create the dot of light you see on the leaves or paper during the experimentation.

This produces and results in a saturation of heat in the area where the dot is located, strong enough to start its own fire. This sometimes takes some time, depending on weather conditions that dictate the power of the sun during the experiment.

Convex lenses can be used in many important innovations and discoveries. Technology that makes the full utility of this novel invention are creations like binoculars, cameras, telescopes, and even glass bottle bottoms.


The magnifying glass, aside from its very useful primary function, is a fun invention to explore. It does, however, present certain hazards which require adult attention so supervision is required to fully explore its capabilities.

If you and the kids are looking for a unique and educational experience that will empower learning through playing, this experiment is certainly recommended for you.

Elena Jones

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