Magnifying Light, Magnifying Heat
Grade Level: 6th to 8th; Type: Physics
Focus some sunlight with a magnifying glass and trap some of sunlight’s shorter waves to see which melts ice faster.
Will an ice cube melt faster out in the open, under the greenhouse effect, or under focused sunlight?
- Pencil and paper three glass or ceramic bowls three pieces of ice, all the same size
- One piece of glass, big enough to completely cover one of the bowls
- One magnifying glass
- Hot, sunny day
- Clock or watch
- On a hot, sunny day (no clouds or this won’t work!), put a piece of ice into each of three bowls. Cover one of the bowls with glass and take them all outside. You might also want to wear sunglasses; this experiment gets pretty bright!
- Put all of the bowls out in the sunlight where they won’t be disturbed. Note the time on the piece of paper.
- Use the magnifying glass to focus the sunlight on one of the pieces of ice that isn’t in the covered bowl. Experiment with the angle of the magnifying glass and the distance—what you want is the smallest, brightest spot possible right on the piece of ice. Be careful! This spot is hot and you can burn yourself with it, or light something flammable on fire.
- Keep the sunbeam focused on the cube of ice and watch all three to see which one melts completely first. Make note of the time when each one melts.
- Think about which ice melted fastest and why. The ice that just sat out in the sun was exposed to the sun’s heat, but less so than the other two. The glass over the second bowl trapped some of the sun’s shorter waves, like the windows of a car or like greenhouse gases. And the third piece of ice had all of the sun’s light focused on it, not just scattered around it.
Terms/Concepts: greenhouse gases, wavelength
References: Science Fair Adventure: Magnifying Light
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