Chapter 7: Sound and Light

Sound and Light Fireworks are an example of sound and light. First you see the explosion. Then you hear the boom. In this chapter you will learn how sound is produced and how light travels.

Section 7.1: What is Sound?

Sound is a form of energy. What is Sound? Sound is a form of energy. Scientists who study sound also study human hearing and the effect of sound on different objects.

How Sound is Produced All sounds you hear are made when matter vibrates. To vibrate means to move quickly back and forth. Example: Bells—When the bell is struck the clapper inside the bell causes the bell to vibrate. Air particles are pushed in the direction that the bell is swinging.

How Sound Travels The movement of air molecules around a vibrating object is a sound wave. You cannot see a sound wave. Sound waves move away from the object in all directions. These waves become weaker as they travel farther away from the object.

Chapter 7.2: Light

Light You see light everywhere. You see objects because light is reflected, or bounced back, from them. Light is a form of energy that you can sometimes see. Most visible light are produced by objects that are at high temperatures. The sun is the major source of light on earth. The sun loses energy by emitting light. The sun’s light arrives in three different wavelengths: visible light, infrared, and ultraviolet radiation.

Light as a Particle Scientists do experiments to gather information about light. Light is made up of bundles of energy called photons. Photons are small particles that are too small to be seen. Each photon carries a certain amount of energy. A beam of light (such as a flashlight) is made up of a stream of photons

Light as a Wave Light travels in waves in a straight line. Most properties of light can be explained in terms of its wave nature. Light waves move like waves in water. Light waves travel fastest through empty space. Light waves move more slowly as they pass through matter. Light waves cannot pass through certain types of matter. Light waves travel more quickly than sound waves. Light waves travel about 300,000 kilometers per second. This is the fastest possible speed anything can travel.

Colors in White Light The light you see from the sun is white light. White light is actually made up of made colors of light. The colors of the rainbow make up white light. The band of colors that you see in the rainbow is known as the visible spectrum. The colors of the visible spectrum always appear in the following order: red, orange, yellow, green, blue, and violet. You can use a prism to see the colors in white light.

Chapter 7.3: How Light is Reflected

What happens when you look into the mirror? Why can you see yourself? How Light is Reflected What happens when you look into the mirror? Why can you see yourself? The answers to these questions lay in the way that light waves act.

Light Bounces When you throw a ball to the floor, it bounces back. Light also bounces back when it hits an object. When light bounces off of an object we say that the light is reflected. Reflection is the bouncing back of a light wave. Few objects give off their own light. We see most objects only because of the light they reflect. An image is a copy or a likeness. An image is visible in a mirror because light waves are reflected.

Types of Mirrors A mirror with a flat, smooth surface is called a plane mirror. The flatter the surface of the mirror, the clearer the image. Many mirrors have curved surfaces. One kind of curved mirror is the concave mirror. A concave mirror has a reflecting surface that curves inward (like the inside of a spoon). A concave mirror creates an image larger than the real object.

Types of Mirrors The reflecting surface of some mirrors (convex mirrors) curves outward (like the outside of a spoon). A convex mirror creates an image that looks smaller than the real object However, you can see much more with convex mirrors (rearview and side-view windows)

Bending Light When light moves from one kind of matter to another, the light waves change speed. As a result, the direction of the light changes. The bending of a light wave as it moves from one material to another is called refraction. Example: Pencil in a glass of water.

Lenses A lens bends light by acting like the water in the container. A lens is a curved piece of glass or other clear material that refracts light waves that pass through it. A concave lens curves inward. The lens is thin in the middle and thick at the edges. Light rays that pass through a concave lens are spread apart. When you look through a concave lens objects appear smaller than they really are.

Lenses A convex lens curves outward. The lens is thick in the middle and thin at the edges. Light rays pass through a convex lens are refracted inward. A convex lens focuses light (magnifies an image).