Light and Sound Waves Explained

Light travels in waves, and sound travels in waves. However, sound waves and light waves are very different, and it is important not to confuse the two. Light travels in electromagnetic waves, and sound does not. Sound waves are caused by vibration.


Electromagnetic Radiation

One way in which energy can be transferred is by electromagnetic radiation. To understand radiation, imagine energy, contained in particles, travelling along in waves. These particles are called photons. Some types of energy are more intense than others, so these photons will move faster. This does not mean that the wave travels faster; all electromagnetic waves always travel at exactly the same speed – the speed of light. But each different type of energy has a different level of intensity and travels at a different wavelength and frequency, with high-energy photons travelling in shorter waves.

Light Waves and Radio Waves are Part of the EMS

The Electromagnetic Spectrum (EMS) encompasses every type of electromagnetic wave, with the high-energy waves at one end of the spectrum and the low-energy waves at the other. At the top end are gamma rays, which have the shortest wavelengths and the highest frequencies, and at the opposite end of the spectrum are radio waves, with the longest wavelengths and the lowest frequencies. In between are microwaves which are slightly shorter than radio waves, then infra-red waves, then visible light waves including ultra-violet, and finally X-rays which are slightly longer than gamma rays.

More About Radiant Energy

Electromagnetic radiation can occur naturally in space. Light reaches us from the sun by radiation; stars emit radio waves. Or it can be originated by man. Radiant energy has an astounding variety of applications, and some of these have had far-reaching consequences; for instance X-rays and ultrasonic waves have both made tremendous contributions to medical science. Low doses of x-rays are used to produce photographic images of tumours, fractures and other conditions, whilst high doses can be used to treat tumours; ultrasonic waves are used in a technique known as ultrasound, to break up kidney stones, and also as a means of scanning organs inside the human body, for instance to produce a ‘scan’ of the baby in the womb during pregnancy.

A very different application of the same principal is the use of ultrasonic waves in sonar devices to track fluctuations in the level of the sea bed. Microwaves are used for cooking food and in mobile phone technology. We build radio transmitters to enable us to communicate over long distances. Electromagnetic radiation has countless applications in engineering, and we are constantly finding new uses for this very versatile phenomenon.

Most forms of radiant energy can only be detected with the aid of some kind of detection device. Visible light is one exception, and infra-red waves are another as they can sometimes be detected as heat. Contrary to popular belief, radio waves are not audible, although they can produce sound waves which are.

Sound Waves are NOT Radiant Energy

As described above, radio waves are a form of electromagnetic radiation. Radio waves can be converted into sound, and sound also travels in waves, but sound waves are not composed of photons. Sound waves are created by the rapid vibration of an object. This vibration can be caused in many ways – by radio waves, by electrical impulses, or by some kind of mechanical means. The to-and-fro movement of the vibration alternately compresses and decompresses the air particles next to it, creating a wave that is composed of ‘compressions’ and ‘rarefactions’. Sound cannot therefore travel through space, where there are no particles to create a sound wave; radio waves can, because they are composed of photons.

Sound waves can travel over a relatively short distance before they fade, depending on the intensity of the sound, whereas radio waves can reach us from space. The speed at which a sound wave travels is around 1,100 feet per second; that’s quite fast, but nowhere near the speed of light, the speed at which radio waves travel, which is around 185,000 miles per second. During a thunderstorm, electrical energy is created, producing light and sound.

The lightning travels to Earth as light waves. The thunder travels as sound waves, produced by the vibration caused by the explosive burst of electricity. So we see the lightning before we hear the thunder, and the time lag between the two increases when the distance travelled is further. This is a good illustration of the difference between electromagnetic waves such as light and radio waves, and sound waves.