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Reflection Refraction Reflection Refraction Why would you have to turn on this desk lamp to use the phone? Could you see in a dark room without any light? Light bounces or reflects off objects and into your eyes. If you held your hands in front of your eyes, you would not be able to see the reflected light from the table or telephone. The light bulb inside the lamp gives off its own light, which reflects off all the surfaces in the room and into your eye. How Light Reflects When light strikes a surface, such as the wall, phone, or table in the picture, light is reflected, or bounced back, allowing it to be seen. When light hits a surface like a glass window, it passes through (is transmitted). If light hits a surface like frosted glass, only some light passes through and the glass scatters the rest. If light strikes an opaque object, it cannot pass through and the object absorbs some of the light. Light is either reflected, transmitted, absorbed—or a combination. For example, objects that are not shiny, like green grass or a red tomato, will absorb all wavelengths of white light, except for the green or red, which it reflects back to your eye. Black objects absorb almost all wavelengths and appear to have no color, while white objects reflect all colors. 1 Reflection Refraction Rule of Reflection Rays of light follow a simple reflection rule: the angle of the incoming ray is equal to the angle of the outgoing ray of light reflecting back. Another way of saying that is the angle of incidence equals the angle of reflection. For example, a flashlight beam will reflect at the same incoming angle. The type of surface affects reflection. Shiny objects do not absorb or scatter wavelengths. Instead, the shiny surface reflects mirror-like images to the observer. Whether the surface is smooth, rough, or curved affects those reflections. On a flat, shiny surface, incoming rays all reflect in the same angle direction and do not scatter. On a rough surface, the incoming rays reflect at different angles and are scattered. Mirror Reflections Mirrors are a very interesting use of reflection. Have you ever wondered how a mirror works? Mirrors are very smooth pieces of glass backed by very shiny, highly polished reflective material. Light travels through the glass and then reflects off of the smooth and shiny surface at the back. When you look in a mirror, you see light from your face reflected off of the mirror. The way light bounces off of mirrors can be predicted. Light reflects from a mirror at the same angle as it arrives. Think about bouncing a ball. If you throw a ball straight at a wall, it will bounce straight back at you. If you throw the ball at an angle, it will bounce off the wall at the same angle away from you. Light reflects the same way off of a mirror. Grab a mirror and a friend and try looking at each other from different angles in the mirror. 2 Reflection Refraction When you look in a mirror, you see a regular image of yourself. The only difference is that your mirror image is flipped from left to right. However, why do you think your image looks distorted in a carnival mirror? Look at the image of the girls in the carnival mirror. Is the mirror flat? Think of other surfaces where you can see your reflection, such as a store window, a chrome bumper, or a monitor screen. Is the reflection true or distorted? Why or why not? Not all images are reflected the same size. Curved surfaces can change reflections. A concave mirror bends inward and magnifies the image. A convex lens bends outward and makes the image look smaller but wider. Flat mirrors reflect an equal image. Now you try testing the reflections on curved surfaces. You will need shiny spoons of several sizes. Look at your image in the bowl of the spoon. What do you see? Is your image upside down or right side up? Next look at your image reflected off the back of the spoon. How does that image compare to the one on the bowl of the spoon? Draw pictures of your observations and record your conclusions. 3 Reflection Refraction How Light Refracts You have learned that light travels in a straight line until it comes to an object or enters a different medium. If light cannot pass through an object, it will be reflected (bounce off), absorbed, or both. When light passes from one kind of material (called a medium) to another, the light slightly changes speed and bends, or refracts. If you put a pencil in water, the light refracts, passing from air through glass and into water, causing the pencil to appear bent. Prisms Refract Light Prisms are solid objects made of glass or plastic with rectangular or triangular ends and rectangular sides. When light shines through a prism, it bends (refracts) and separates into a rainbow of colors. White light is made up of many different wavelengths that bend at slightly different angles. Long wavelengths, like red, bend the least while blue wavelengths bend the most. Sunlight is made up of all wavelengths of visible light. When light passes from the air into water, such as a raindrop, the different color wavelengths slow down (because water is denser than air), bend at different angles (refract), and separate. The result is a rainbow––a colored arc of light. Lens makers take advantage of this property of light and form curved lenses to change the path of light rays. Changing the path of light can improve vision when glasses or contact lenses are worn. 4 Reflection Refraction 1. Why does this green laser light reflect off the mirror at that angle? 2. What is the difference between light that is absorbed and light that is transmitted? 3. Why does a curved mirror change the way an image is reflected? 4. Why do you see an apple as a red color? 5. Compare the way light acts with a white object to the way it acts with a black object. 6. Why does a straw look broken when placed in a glass of water? 5 Reflection Refraction Mirror, Mirror on the Wall To help your child understand how mirrors Here are some questions to reflect light, take a car trip around your discuss with your child: town. Look for different ways mirrors are 1. Does the incoming light angle used by observing the reflections in these match the outgoing light angle? different types of mirrors: 2. Why does that mirror create that type of reflection? Try these sources: 3. Does the surface have to be • Clothing store mirrors shiny to create a mirror image? • Makeup mirrors 4. Why do school buses need • Dentist’s hand tool mirror special side mirrors? • Car rearview mirror • Car side mirror • Semi-truck mirror • Building corner mirror • Security mirrors • Pocket mirrors • House of Mirrors at a carnival • Mirror store • School bus mirror 6.
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