From Scientific American:
Light is fascinating! It can look like a wave or a particle; it can be red, blue or any color of the rainbow; you can even mix all the colors together to get white! It travels in straight lines and still appears to bend around objects. It can travel through air but it does not need it. Unlike sound, light can travel from distant stars through a vacuum and reach us millions of years later or it can be sent through fiber-optic cables and circle the world in less than a second! Does that sound impressive? How about pouring light from a bottle into a glass or sink? Does this sound too far-fetched to you? Try this activity and make it happen!
Have you ever noticed how you need to point a flashlight toward an object to illuminate it? That shows light travels in straight lines. But what if we introduce a mirror or shine a light beam into water? Light bouncing off a shiny surface (in other words, reflected by the surface) or light bent when entering a medium (meaning refracted by the surface) introduces kinks into these straight lines. (Several activities listed in the “More to explore” section below can help you understand these phenomena better.)
In this activity you will look at what happens when light inside a body of water reaches the water’s surface. Light falling nearly perpendicular on a water–air surface pierces through it; that is why we call water “translucent.” But did you know that water also reflects part of the light? It almost acts like a mirror for light hitting it at small angles with the water’s surface. When light initially hits the water-beam boundary at a small angle, it keeps hitting the boundary at small angles and is reflected over and over …