What is Electromagnetic Radiation?

Electromagnetic radiation is energy in waves (like visible light), emitted from a source. The energy is both electrical and magnetic. The wave alternates rapidly, from positive to negative in electrical terms and from North to South in magnetic terms.

Electricity and magnetism are very closely related in nature. For example, when an alternating magnetic wave penetrates a body (including yours!) an alternating electric current is generated within it.

Electromagnetic radiation from a source penetrates the surrounding area, creating an electromagnetic field (EMF). This EMF is strongest at the source, and weakens with increasing distance until it becomes imperceptible.

Some of the important properties of electromagnetic Radiation are its Frequency, Wavelength and Intensity.

Frequency, Wavelength and Intensity

The frequency of a wave tells us how fast the wave oscillates (in cycles per second, also called Hertz or Hz). A cycle is one oscillation of the wave (one peak and one trough).

The range of all frequencies of electromagnetic radiation is collectively known as the Electromagnetic Spectrum.

Wavelength

The wavelength of a wave is the distance between two successive wave crests. Wavelength is inversely proportional to frequency - the higher the frequency, the shorter the wavelength.

Electromagnetic wavelengths of interest to us span a huge range - from about 5000 km (long wave) to 1 millimeter (microwave).

Intensity

In practical terms, the intensity or strength of an electromagnetic field at any particular point depends upon

• the amount of electrical and magnetic energy radiating from its source
   
• the distance from that source
   
• the extent to which the radiation has been absorbed (or blocked, or shielded).

The electric field and magnetic field components of the EMF can be separately measured.

Electrical field strength can be measured in volts per metre (V/m) or as power density in milliwatts per square centimeter (mW/cm²⁾.

Magnetic fields can be quantified in milligauss (mG) or microTesla (1 microTesla = 10 milliguass).

Electromagnetic Spectrum

In the electromagnetic spectrum, frequencies range from less than 20 Hz to 100 000 000 000 000 000 000 or 10²⁰ Hz

The visible light spectrum is a portion of the electromagnetic spectrum. Visible light ranges from 10¹²Hz to 10¹⁶Hz

Because of their potential effects on our health, we are most concerned with the lower electromagnetic frequencies (20 to 10¹² Hz). This range includes

Extremely Low Frequencies, or ELF    (<100 Hz)
Very Low Frequencies, or  VLF     (100 Hz to 10 kHz)
Radio Frequencies, or RF            (10 kHz to  300 MHz)
Microwaves.                            (300 MHz to 1000GHz)

These waves are now very prevalent in our environment.

The reason why we are not concerned with X-Rays and Gamma rays (which are in fact the most dangerous forms of EM radiation) is that our exposure to these rays is (or should be) very occasional.

Low Frequency EMF (ELF and VLF)

The ELF band includes the important power line frequency (60 Hz in US and 50 Hz elsewhere) which contributes greatly to our electromagnetic pollution. Power lines, house wiring and electrical appliances all create EMFs of this frequency.

An electrical appliance may emit electromagnetic radiation at more than one frequency. For example, a washing machine on spin cycle would emit an EMF of 60 Hz (the supply frequency) as well as an EMF related to the speed of the electric motor driving the spinning drum.

At these low frequencies it is still possible to separate the electrical and magnetic components of the EMF. (At higher frequencies it is not practical to do so).

An electric field may be created by an electrical appliance (or rather, its supply wire) if it is connected to mains electricity, even though the appliance itself may not be switched on.

When the appliance is switched on and a current actually flows through it, the appliance (and its supply wire) will generate a magnetic field as well as an electric field. (A magnetic field is always generated when an alternating electrical current flows).

For low frequency EMFs, the electric field is easily shielded, even by flimsy screening. But the magnetic field penetrates most materials, including brick or concrete walls. It has no trouble penetrating a human body.

Because of this penetration, the magnetic field is the more important component of low frequency EMF, so this is the component that is usually measured - in milligauss (mG).  

Radio Frequency EMF

 The radio frequency band includes AM and FM radio and TV (VHF) transmissions.

For this type of EMF, the magnetic field strength is proportional to the electric field strength. Both are equally penetrating. If you know the magnetic field strength, you can calculate the electric field strength, and vice versa.

It's easier to measure the electric field, so the intensity is quantified in Volts per metre (V/m).

Microwave EMF

The microwave band includes radiation from cell phones, cell phone towers, other communications systems and microwave ovens.

As for Radio waves, the magnetic field strength is proportional to the electric field strength, so we measure the electric field strength in Volts per metre (V/m)

These are very high energy waves.

Wave modulation

Electromagnetic waves may be modulated to encode a digital or analog signal. This is how radio and microwave frequencies can be used to transmit audio or video information.

Radio and TV transmissions, as well as cell phone communications, all use a modulated signal on top of a basic 'carrier' wave.

In the case of these modulated waves, it appears that the encoded signal itself (apart from its carrier wave) is a possible source of biological effects.

Natural radiation shielded by Earth’s atmosphere

In general, Earth’s atmosphere protects us by absorbing most of the electromagnetic frequencies present in the cosmos, except for lower frequency radio waves and visible light rays.

So animals and humans evolved in an environment where many wavelengths were either not present at all, or were fleetingly present at low intensity.

That is why we have not developed protective mechanisms against them.

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Disclaimer: This material has been provided for information only. It is not sufficient to enable you to self treat any medical condition. If you have a medical condition, please consult your healthcare professional.  

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What is Electromagnetic Radiation?