How does using sunlight through a magnifying glass to start a fire work and how does it not violate the whole we can never create more energy then we put into it equation?
In: Biology
The energy is coming from the light source – the sun.
Every kind of matter that light can pass through without scattering, be it water, air, crystals, glass, whatever, bends the light. We know that as refraction. Light can pass through, say, a sheer piece of fabric, but from there, it’s not bent, but scattered, so we can’t see the stuff that’s not blocking the light on the other side. When light is refracted, it all gets bent the same way (mostly. There’s a tl;dr that could be added here). So a lens that bends light toward its center if held at exactly the right distance from an object, will cause all the light that would hit the area of the lens to hit a much smaller area. If regular sunlight can warm your body, it follows that more sunlight in the same area should heat that spot up more. If you use some dry grass or something, there can be enough heat to start burning it. And a fire is born.
Sorry if this is more ELI5 than you meant. Just wanted to make sure I covered the basics.
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