Refraction of Light Notes

Refraction of Light Knowtty: Today, we're going to learn about the Refraction of Light. Light is a form of energy that helps us see. It's a big part of our daily lives. And it can also do some cool things like reflect, bend and interfere. Let's now focus on refraction-something that happens all the time, even if we don't notice it! Rinku: A straw looks bent in a glass of lemonade. Why does that happen? Knowtty: Excellent observation. What you're seeing is refraction. It happens because light travels at different speeds in different materials. When light moves from one material to another, its speed changes. This causes light to bend or deviate. In the case of the straw, light travels from air (a less dense medium) into water (a denser medium). And it makes the straw appear bent at the surface of the liquid. Reema: Oh, so the straw looks bent because light slows down and bends when it enters water! But how does light know where to bend? Knowtty: Good question, Reema. It's all about optical density. The optical density of a material is how much it slows down light. → In denser materials, light travels more slowly. When light enters a denser material like water, it slows down and bends. If light moves into a less dense material like air, it speeds up and bends the other way. Let me now give you a simple summary of this. Concepts of Refraction Refraction: When a ray of light enters obliquely from one transparent medium to another, Its path undergoes a deviation at the surface of separation. This is refraction. When light enters from one medium to another, the Incident ray, the refracted ray, and the normal at the point of Incidence are all on the same plane. When light enters from an optically rarer medium into a denser medium, it deviates towards the normal. When light enters from an optically denser medium into a rarer medium, it deviates away from the normal. How do we see things? We see things because light falls on them, gets reflected, and then travels to our eyes. Light travels at different speeds in different media Light travels at different speeds in different materials. For example, it travels faster in air than in water or glass. Optical Density The ability of a material to affect the speed of light is called its optical density. The denser the material, the slower light travels through it As the optical density of a medium increases, the speed of light through it decreases. And as the optical density decreases, the speed of light Increases. When light moves from Air to Glass If light enters from a medium of lower optical density (air) into a higher optical density (glass), it bends towards the normal. When light moves from Glass to Air If light enters from a denser medium (glass) into a less dense one (air), it bends away from the normal. Refractive Index The refractive index of a material tells us how much light bends when it enters that material. It is the ratio of the speed of light in air to the speed of light in the material. Critical Angle and Total Internal Reflection The angle of incidence in the denser medium at which the angle of refraction becomes 90° is called the critical angle. If the angle of incidence Is greater than the critical angle, total internal reflection happens. And the light bounces back into the denser material. Applications of Total Internal Reflection Optical fibres, prism periscopes, bicycle reflectors and endoscopes use total internal reflection.