demonstrations:burning_paper_with_a_convex_lens
Burning Paper with a Convex Lens
Materials: ★☆☆ Easy to get from supermarket or hardware store
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★★☆ Some safety precautions required to perform safely
Categories: Light
Alternative titles: Focusing Sunlight with a Convex Lens
Summary
A convex lens is used to concentrate sunlight onto a small point on a piece of paper. The focused light intensifies the heat at the focal point until the paper ignites.
Procedure
- Put on sunglasses for eye protection (Note: do not look at sun directly or through convex lens).
- Take the experiment outdoors on a sunny day.
- Place a sheet of paper on a flat, safe surface.
- Hold the convex lens above the paper so sunlight passes through it.
- Adjust the distance between the lens and paper until the light forms the smallest, brightest spot possible.
- Keep the focal point steady on the paper until it begins to smolder and burn.
- Extinguish the fire once the demonstration is complete.
Links
CONVEX LENS AS BURNING GLASS - Make Me Scientific:
📄 Burning up the Paper with a Magnifying Glass - RonyesTech: https://www.ronyestech.com/2020/05/burning-up-paper-with-magnifying-glass.html
Variations
- Try using different colors or thicknesses of paper (darker paper burns more easily).
- Experiment with different sizes or curvatures of convex lenses.
- Test if artificial light sources (like a strong lamp) can focus enough energy to burn paper.
Safety Precautions
- Perform only outdoors in a clear area, away from flammable materials.
- Wear sunglasses to protect your eyes from bright concentrated light.
- Always supervise children during this activity.
- Extinguish any flames immediately after the demonstration.
Questions to Consider
- Why does the convex lens make sunlight more intense? (Because it focuses parallel rays of sunlight to a single point, concentrating the energy.)
- Why does darker paper burn more easily than white paper? (Dark paper absorbs more light energy, converting it to heat faster.)
- Could ordinary flat glass burn paper the same way? (No, because it does not converge light to a focal point like a convex lens does.)