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These contents were downloaded form world Health organization websitehttp://www.who.int/peh-emf/about/WhatisEMF/en/index3.html For moredetails Refer the website given above

Introduction to Electromagnetic Fields

Sources of Electromagnetic fields

Natural sources of electromagnetic fields

Electromagnetic fields are present everywhere in our environment butare invisible to the human eye. Electric fields are produced by the localbuild-up of electric charges in the atmosphere associated withthunderstorms. The earth's magnetic field causes a compass needle toorient in a North-South direction and is used by birds and fish fornavigation.

Human-made sources of electromagnetic fields

Besides natural sources the electromagnetic spectrum also includesfields generated by human-made sources: X-rays are employed todiagnose a broken limb after a sport accident. The electricity thatcomes out of every power socket has associated low frequencyelectromagnetic fields. And various kinds of higher frequency radiowaves are used to transmit information whether via TV antennas,radio stations or mobile phone base stations.

What is the difference between non-ionizing electromagnetic fields andionizing radiation?

Wavelength and frequency determine another important characteristicof electromagnetic fields: Electromagnetic waves are carried byparticles called quanta. Quanta of higher frequency (shorterwavelength) waves carry more energy than lower frequency (longerwavelength) fields. Some electromagnetic waves carry so much energyper quantum that they have the ability to break bonds betweenmolecules. In the electromagnetic spectrum, gamma rays given off byradioactive materials, cosmic rays and X-rays carry this property andare called 'ionizing radiation'. Fields whose quanta are insufficient tobreak molecular bonds are called 'non-ionizing radiation'. Man-madesources of electromagnetic fields that form a major part of industrialized life - electricity, microwaves and radio frequency fields are found at the relatively long wavelength and low frequency end of the electromagnetic spectrum and their quanta are unable to breakchemical bonds.

http://www.who.int/peh-emf/about/WhatisEMF/en/index3.htmlhttp://www.who.int/peh-emf/about/WhatisEMF/en/index3.html

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Difference between Electric and Magnetic field

Electric fields Magnetic fields

1. Electric fields arise fromvoltage.

2. Their strength is measuredin Volts per metre (V/m)

3. An electric field can bepresent even when adevice is switched off.

4. Field strength decreaseswith distance from thesource.

5. Most building materialsshield electric fields tosome extent.

1. Magnetic fields arise fromcurrent flows.

2. Their strength is measuredin amperes per meter(A/m). Commonly, EMFinvestigators use a relatedmeasure, flux density (inmicrotesla (T) or millitesla(mT) instead.

3. Magnetic fields exist assoon as a device isswitched on and currentflows.

4. Field strength decreaseswith distance from thesource.

5. Most materials do notattenuate magnetic fields.

Classification of Electromagnetic Waves

Static (0 Hz)Extremely low frequency (ELF, >0-300 kHz)Intermediate frequencies (IF, >300Hz to 10MHz)Radio frequency (RF, 10 MHz-300 GHz) fields

Electromagnetic Fields and Health problems

Electromagnetic fields and cancer despite many studies, the evidencefor any effect remains highly controversial. However, it is clear that if electromagnetic fields do have an effect on cancer, then any increase

in risk will be extremely small. The results to date contain manyinconsistencies, but no large increases in risk have been found for anycancer in children or adults.A number of epidemiological studies suggest small increases in risk of childhood leukemia with exposure to low frequency magnetic fields inthe home. However, scientists have not generally concluded that theseresults indicate a cause-effect relation between exposure to the fieldsand disease (as opposed to artifacts in the study or effects unrelated to

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frequencies have much lower energy that do not have thisability.

4. Electric fields exist whenever charge is present and aremeasured in volts per metre (V/m). Magnetic fields arise fromcurrent flow. Their flux densities are measured in microtesla (T)

or millitesla (mT).5. At radio and microwave frequencies, electric and magnetic fieldsare considered together as the two components of anelectromagnetic wave. Power density, measured in watts persquare metre (W/m 2), describes the intensity of these fields.

6. Low frequency and high frequency electromagnetic waves affectthe human body in different ways.

Electrical power supplies and appliances are the most common sourcesof low frequency electric and magnetic fields in our living environment.Everyday sources of radio frequency electromagnetic fields aretelecommunications, broadcasting antennas and microwave ovens.

Thanks for the World health organization for taking the EMF healthproblems as a major issue and sponsoring for research in the area of EMF health Problems

M. SenthilKumaran