Electromagnetic Spectrum: Sources and Uses of Radio Waves

Introduction:

A changing electric and magnetic field, produced by a moving charged particle, generates an electromagnetic wave. Like all waves, electromagnetic waves have some general properties like wavelength, frequency, and speed. The continuous range of frequencies of electromagnetic radiation is divided up into different wave types.

Explanation:

Electromagnetic Spectrum:

The entire range of wavelengths of electromagnetic radiation or the components of electromagnetic waves is arranged according to characteristics such as frequency, known as the electromagnetic spectrum.

The electromagnetic spectrum is a wide range of electromagnetic waves with different wavelengths and frequencies. The spectrum is divided into different parts. Figure-1 shows the names of the different waves that make up different parts of the spectrum.

Different types of electromagnetic waves travel at the same speed in a vacuum, at the speed of light. The waves travel at the same speed, so the frequency of electromagnetic waves increases as their wavelength decreases.

Radio Waves:

Electromagnetic waves with wavelengths longer than about 0.001 m are called radio waves. Radio waves have the lowest frequencies of all electromagnetic waves. They also carry the least energy.

Example: Television signals and AM and FM radio signals are types of radio waves.

Source of Radio Waves:

Radio waves are produced by moving charged particles. One way to make radio waves is to make electrons vibrate in a piece of metal. This piece of metal is called an antenna. The vibrating electrons in an antenna cause radio waves to move outward from the antenna. By changing the speed of electron vibrations, radio waves of different frequencies can be generated.

Receiving Radio Waves:

Radio waves can cause electrons in another antenna to vibrate. Vibrating electrons in a receiving antenna form an alternating electric current. This current can be used to produce a picture on a TV screen and sound from a loudspeaker.

Changing the frequency of the waves changes the alternating current in the receiving antenna. This produces the different pictures and sounds we hear on our TV.

Uses of Radio Waves: Radar

Radar uses electromagnetic waves to detect objects in this way. Radar stands for Radio Detection And Ranging. A radar station sends out radio waves that bounce off things such as airplanes. Electronic equipment receives the reflected signals. The equipment measures the time it takes for the waves to return. Because the speed of the radio waves is known, the distance from the airplane to the object can be found from the measured time.

Microwaves:

Radio waves with wavelengths from about 0.3 m to 0.001 m are called microwaves. Microwaves have a higher frequency and shorter wavelength than the waves used in our home radio. Cellular and portable phones use microwaves.

Uses of Microwaves:

Microwave ovens use microwaves to heat food. Microwaves cause water molecules in the food to vibrate. As the molecules vibrate faster, the food becomes warmer.

Infrared Waves:

The heat you feel is from electromagnetic waves called infrared waves. Infrared waves are electromagnetic waves with wavelengths between one thousand and 0.7 millionths of a meter.

Most electromagnetic waves generated by an object at room temperature are infrared waves. Infrared detectors can detect infrared waves from objects that are warmer or cooler than their surroundings.

Visible Light:

When an object gets warmer, its atoms and electrons vibrate faster and faster. The vibrating electrons produce electromagnetic waves. Some of the electromagnetic waves the object gives off or emits can be seen. These electromagnetic waves are known as visible light.

Visible light has wavelengths between 0.7 and 0.4 millionths of a meter. The different colors you see are electromagnetic waves with different wavelengths. Red light has the longest wavelength. Blue light has the shortest wavelength.

Ultraviolet Radiation:

Ultraviolet radiation is higher in frequency than visible light and has even shorter wavelengths, between 0.4 millionths and about 10 billionths of a meter. Ultraviolet radiation also carries more energy.

Dangers of Ultraviolet Radiation:

The radiant energy transferred by an ultraviolet wave can damage or kill living cells. Too much exposure to the Sun’s ultraviolet waves can cause sunburn. Exposure to these waves over a long period can cause the skin to age and might cause skin cancer.

Advantages of Ultraviolet Radiation:

Our body uses ultraviolet radiation from the Sun to produce vitamin D. A few minutes of sunlight each day is enough to produce all the vitamin D our body needs.

Ultraviolet radiation can kill cells; it is used to disinfect objects such as surgical instruments and goggles.

Ozone Layer:

Ozone is a molecule that contains three oxygen atoms. It is formed high in the Earth’s atmosphere. The ozone layer absorbs most of the ultraviolet radiation from the Sun before it reaches the Earth’s surface.

The Earth’s atmosphere also absorbs other types of electromagnetic radiation. It absorbs higher energy waves like X-rays and gamma rays. Radio waves, light waves, and some infrared waves can pass through the atmosphere.

X-Rays:

X-rays have a higher frequency than ultraviolet rays and have enough energy to go through skin and muscle. A shield made out of a dense metal such as lead is needed to stop X-rays.

Uses of X-rays:

X-rays can pass through the less dense tissues of skin and muscle. X-rays strike a film and leave shadow images of bones and denser tissues, like the one in the figure below. Doctors use X-ray images to find injuries and diseases such as broken bones and cancer.

Gamma-ray:

Gamma rays have the highest frequency and carry the most energy. Gamma rays are the hardest to stop. They are produced by changes in the nuclei of atoms. In nuclear fusion, protons and neutrons bond together. In nuclear fission, protons and neutrons break apart. In both of these reactions, huge amounts of energy are released. Some of this energy is released as gamma rays.

Uses of Gamma Rays:

A beam of gamma rays can be used to kill cancerous bacteria in food. The penetration power of gamma rays is very high. As they have high frequency and energy.