Electromagnetic Waves

Electromagnetic Waves

Although you might not know it you’re constantly surrounded by thousands of electromagnetic waves every day. Sunlight and x-rays are only two types of electromagnetic waves, other types are: radio wave, infrared rays, ultra-violet rays and gamma rays

Nature of an electromagnetic wave Electric and magnetic fields are not made up of matter. An electromagnetic wave consists of an electric and magnetic field and doesn’t need a medium to exist. They are the regions through which the push or pull of charged particles and magnets is exerted. The magnetic field and an electric field positioned at right angles to each other and to the direction of motion of the wave. Because of this they are transverse waves.

Production and Transmission of Electromagnetic Waves The source of all electromagnetic waves is charge that is changing direction or speed.

The Electromagnetic Spectrum

Electromagnetic waves are arranged in order of wavelength and frequency in what is known as the electromagnetic spectrum. It ranges from very long wavelength and low frequency to very short wave length. The amount of energy carried by an electromagnetic wave increases with frequency.

1) Radio Waves: The waves in the electromagnetic spectrum that have lowest frequencies and longest wavelengths are called radio waves. They are produced when charged particles move back and forth in instruments such as a antennas. When radio waves are transmitted, one of the characteristics of the wave can be varied: the amplitude or frequency of the wave. This variation is called modulation. The setting on your radio indicates the type of modulation used to carry the information to your radio: AM means amplitude modulation and FM means frequency modulation.
Microwaves: One particular group of radio waves is that of microwaves. Microwaves are the highest frequency radio waves, the wavelengths are only a few centimeter long.
Radar: Short wave length microwaves are used in radar. They are used to locate and monitor speed.

2) Infrared Rays: Electromagnetic waves with frequencies slightly lower than visible light are called infrared rays. Although infrared rays can’t be seen the can be felt as heat. Nearly 50% of the rays emitted by the sun are in the infrared region. All objects give off infrared rays. The amount of infrared rays given off by an object depends on the temperature of the object. The warmer they are the more infrared rays they give out.

3) The Visible Spectrum: The electromagnetic waves that you can see are called visible light.

4) Ultraviolet Rays: Electromagnetic wave with frequencies a bit higher than visible light are called ultraviolet rays. The energy of ultraviolet rays is great enough to kill living cells. That’s why ultraviolet lamps are often used to kill germs destroy bacteria and preserve food.

5) X-rays: Electromagnetic waves with frequencies just above ultraviolet rays are called x-rays. The energy is great enough to pass easily through many materials including your skin, denser materials absorb them like bones.

6) Gamma Rays: Electromagnetic waves with the highest frequencies and the shortest wave lengths are called gamma rays. They have the highest energy of the electromagnetic spectrum. Certain radioactive materials and nuclear reactions emit gamma rays. They have tremendous penetrating ability so great that they can go through three meters of concrete. Excessive exposure can cause severe illness .

Visible light

Certain organisms and objects give off their own light. Anything that can give off its own light is called a luminous object. The sun, and other stars, light bulbs, and fire flies are luminous objects. Other objects are lit up but not by their own light. An object that can be seen because it’s lit up is called an illuminated object.

Production of Light

A luminous object can produce incandescent light fluorescent light or neon light.
Incandescent light: Light that is produced from heat is called incandescent light.
Fluorescent Light: Its cooler and uses much less electricity than incandescent light. Instead of being used to build up heat, electrons are used to bombard molecules of light kept at low pressure in a tube.
Neon light: It’s similar to fluorescent light because it’s cool. When electrons pass through the tubes filled with certain gases light is produced. The most common type of gas is neon gas. The light produced from it is bright red. If other gases are added different colors are produced.

Wave or particle?

In the early 1900’s scientists discovered something that made them modify the wave theory. Scientist showed violet light unto the surface of certain metals. The energy carried by the light was absorbed by electrons in the atoms of the metal plate. This energy knocked electrons out of some of the atoms in the metal plate. In fact, enough electrons were knocked off it too cause an electron current to flow. Each individual particle would be a tiny bundle of energy related to the amount of energy absorbed by an electron. Each individual bundle or photon of red light acting on its won could never knock an electron from its atom. Further experimenting showed that photon energy increases as frequency increases and wavelength deceases. Thus photon energy increases across the electromagnetic spectrum from radio waves to gamma rays. Because the experiments involved both electrons and photons the outcome came to be known as photoelectric. Scientists today describe light and other electromagnetic waves as both particle like and wave like. Remember science is a way of explaining observations it’s not absolute knowledge.

Bibliography
Prentice Hall Physicasl Science edition 1996

Bibliography: Prentice Hall Physicasl Science edition 1996