WaveLightScience

Energy is often transmitted or transferred in the form of waves. A wave is a series of back and forth or up and down vibrations. The energy in a wave travels but the material that the wave travels through only vibrates. A boat bobs up and down as waves pass. The boat moves at right angles to the direction of the waves. This is an example of transverse waves. Light, television, radio, and x-rays are transverse waves. Sound is an example of a longitudinal wave. In longitudinal waves, the material that the wave is traveling through vibrates parallel to the direction of the wave.

The speed of light is accepted today as approximately 300,000 kilome-ters per second in a vacuum. This is equal to about 186,000 miles per second. In a more dense medium, such as glass, light will slow down, causing a change in the direction of the wave. This change of direction of waves as they pass in a slanted path from one medium to another is called refraction.

Refraction enables us to bend and focus light, making telescopes, cameras, and microscopes possible. Prisms allow us to separate visible light in the various wavelengths we see as colors.

Color. White light is actually a group of wave-lengths and frequencies. Each frequency is re-fracted differently as it passes from air into glass and from glass into air again. The higher fre-quencies are refracted more than the lower ones. Violet is refracted most, followed by blue, green, yellow, orange, and red.

Rainbows are caused by the refraction of sun-light by raindrops. Rainbows are usually visible when the sun and rain are opposite each other and the sun is low in the sky. Usually, we must be facing the falling rain with the sun behind us to see a rainbow. In addition, the raindrops must be of a certain size to act as tiny prisms.

The color that an object appears to be depends on the frequency of the light that reaches the eye from that object. A red apple appears red because to our eyes it reflects only red light. It absorbs all other colors of light. If the same apple were placed in green light, it would appear black to us. The apple would absorb the green light; since there would be no red light to reflect, it would appear black. This is true for all opaque objects. Opaque objects do not allow light to pass through.

Transparent objects, such as glass, do allow light to pass through. They appear to be the color of the wavelength of light that passes through them. Green glass transmits or sends through light in the green frequency range and absorbs or filters out other colors.

The sky appears blue to our eyes when the particles of dust and gas in the atmosphere scatter the wavelengths of blue light. During midday, when the sun is most directly overhead, its light passes through a minimum of atmosphere. The light we receive appears white. The sun is close to the horizon in the evening and morning. Its light passes through more atmosphere. Dust particles in the air block off or scatter the shorter (blue) wavelengths of light and the sky around the sun appears to be orange or red.

Sound is produced when an object is made to vibrate (move rapidly back and forth). We perceive these vibrations as sounds when they are transmitted by our ears to our brains. Sound requires a medium; that is, a substance to carry the energy. A medium can be a solid, liquid, or gas. Sound is transmitted when the vibrating object disturbs the particles that make up the medium. When an object is made to vibrate, it collides with the particles of the medium. These particles receive energy from the vibrating object and pass the energy to the particles with which they collide. The energy of the vibrating object is transferred to particles around it with each back and forth movement. In this way, sound is transmitted in all directions.

The speed of sound depends on the density of the medium through which it is traveling. In general, sound has a greater velocity in solids than in liquids or gases. The rate at which vibrations of an object are produced is called the frequency of that sound. Frequency is the number of cycles per second. A cycle is one sound wave. One hertz is equal to one cycle per second.

The human ear can detect sounds from about 20 hertz to 20,000 hertz. Sounds with a greater frequency than 20,000 hertz are called ultrasonic. Pitch is the highness or lowness of a sound. Pitch is related to frequency in that the greater the frequency, the higher the pitch produced.

Wavelength is also related to the pitch. The wavelength is the length of one cycle. Greater frequency means a shorter wavelength and a higher pitch of the sound produced. The amplitude of a sound wave is the distance that the par-ticles of the medium were displaced. Greater amplitude means a greater intensity, or loudness, of the sound produced.