Grassmann's law (optics)

Grassmann's law is like a rule that helps us figure out how light behaves when it passes through materials that bend or refract it. When light rays enter a bendy material like glass or water, they change direction, and this can make it tricky to figure out what's going on. But Grassmann's law tells us that the total amount of light that goes into the material will always equal the total amount of light that comes out of it.

Think of it like a slide at a playground. If we have a bunch of people at the top of the slide, and they all slide down at different angles, they'll end up in different places at the bottom. But no matter where they end up, the total number of people coming out of the slide will always be the same as the total number of people who went in. It's a bit like that with light passing through bendy materials - it might bounce around a bit and end up in different places than where it started, but the total amount of light will always be the same.

Grassmann's law is really helpful for scientists and engineers who are designing things like cameras and microscopes, where they need to make sure that the light behaves predictably and consistently. By knowing that the total amount of light won't change as it passes through a material, they can make accurate calculations about things like focus and magnification.