How Light Bends> Transparent objects let light pass through them. Try it: In a dark room, shine a flashlight straight through an aquarium full of water. The light travels through the air, through glass, through water, through glass, and through air again. Right?
All those changes, air to glass to water to glass to air, take a toll. Each time light travels from one medium (like air) to another (like water), it bends, or <#5646,5119><!refracts>.
Now shine the flashlight through the glass at different angles. Try it from the bottom, pointing up toward the surface. Try it from the top looking down. Where does the beam come out on the other side? For a better view, hold a piece of paper near the aquarium to catch the light beam. Another way to see the beam better is to clap two chalkboard erasers nearby. The dust makes the beam more visible.
When light rays strike a transparent material like water head on, they just continue on through the water. But if instead they hit the water at an angle, something else happens. The rays of light all bend a bit away from the surface and towards the straight-on direction. They have taken a new direction to travel. When they leave the water and go back to air, they bend again - this time back the other way. These bends, or changes in direction, when light moves from air to water or glass are called refraction.
Now I’ll throw you a curve. Fill a straight-sided, round glass with water. Shine a light through the curved part. What happens to the beam? The light bends more where it hits the curve of the glass, and less where it hits straight on. The result is that the light rays are bent towards a focus, just like with the concave mirror. You have made a lens!
