READ: Waves and Mediums

READ: Waves and Mediums

Waves come in many shapes and sizes. Light waves transmit energy in the form of light and do not require a medium. Mechanical waves transfer energy through matter by moving particles. Sound waves and water waves are examples of mechanical waves. Waves, both light and mechanical, can be transmitted through various mediums. They can also be reflected and absorbed.

Waves and Sight

Light waves are a type of wave that help us see. Like water waves, light waves also transfer energy. To understand how light waves help us see, look at the illustration.

We see an image when waves of light bounce off of the object and enter our eye. In this way, light waves transfer light energy.

Have you ever turned out all the lights in a room and then tried to walk around? You probably noticed it was a little difficult to see things. That is because there are no light waves present to bounce off the objects around you. Which shows your eyes are useless without light.

Reflection of Waves

When a light ray strikes a reflecting surface the light ray is bounced back in a different direction (reflected). Sound waves can also be reflected. Echos are an example of reflecting sound waves.

Diffuse reflection makes something look dull where regular reflection makes something look shiny because of the way the light waves are reflected.

Sound

Sound is defined as the transfer of energy from a vibrating object in waves that travel through matter. Most people commonly use the term “sound” to mean what they hear when sound waves enter their ears.

Sound waves are mechanical waves. Sound waves begin with vibrating matter. Consider a guitar string. Plucking the string makes it vibrate. The diagram shows the wave generated by the vibrating string. The moving string repeatedly pushes against the air particles next to it, which causes the air particles to vibrate. The vibrations spread through the air in all directions away from the guitar string as waves.

Transmitting Waves

Most of the sounds we hear reach our ears through the air but sounds can also travel through liquids and solids. If you swim underwater—or even submerge your ears in bathwater—any sounds you hear have traveled to your ears through the water. Some solids, including glass and metals, are very good at transmitting sounds. Foam rubber and heavy fabrics, on the other hand, tend to muffle sounds. They absorb rather than pass on the sound energy.

Visible light consists of a range of wavelengths. The wavelength determines the color that the light appears. Light with the longest wavelength appears red and light with the shortest wavelength appears violet. In between is the spectrum of the other colors of light.

A prism, like the one in the figure, can be used to separate white (visible) light into its different colors. A prism is a pyramid-shaped object made of transparent matter, usually clear glass. It transmits light but slows it down. When light passes from the air to the glass of the prism, the change in speed causes the light to bend. Different wavelengths of light bend at different angles. This causes the beam of light to separate into light of different wavelengths. What we see is a rainbow of colors.

Absorbed Waves

When a wave’s energy is transferred to an object, rather than being transmitted through the object or reflected by it, we say the wave has been absorbed. Sound proof walls absorb sound waves. Black material absorbs some of the energy of the sun’s light waves which explains why dark materials heat up in the sun.

The image above shows how a wave can be either absorbed, transmitted, or reflected depending on which medium it is traveling through.

Waves in Everyday Life

Each year there are firework displays all over the United states to celebrate the Fourth of July. Thanks to waves, millions of people are able to enjoy the fireworks displays.Can you explain why waves are necessary to experience fireworks?

You hear the fireworks because sound waves travel to your ears. You see the fireworks because the light waves are detected by your eyes.

The fireworks can be seen before we hear their sound. Why? Light waves travel faster than sound waves.

Sound waves travel at different speeds, depending on the medium through which they are moving. Have you ever seen a Western movie where the hero puts his ear on the railroad track to determine whether or not a train is coming? Why does he put his ear on the track? Sound waves travel faster through solids than they do through gases. The solid steel railroad tracks transmit the train’s rumblings faster than the air does. In general, the more rigid the matter, the faster sound travels through it. Therefore sound travels faster through solids than through liquids and faster through liquids than gases.Can you think of another example of where you’ve seen, felt or heard waves.

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