Invisible lines of force are produced by electrical charges. The electric fields are regions where invisible lines of force produced by presence of ELECTRIC CHARGE or POTENTIAL is experienced or measured.
Static electricity Is a good example of effects of electric fields. We learned in primary science classroom, that by rubbing a piece of ebonite or glass with silk, the ebonite can attract small pieces of paper (invisible lines of force).
The ebonite is said to be electrically charged by the rubbing action. The electric field surrounding the charged ebonite is of constant polarity.
Electric fields are present whenever there is electricity. Much like magnetic fields, if the electricity is alternating (AC), the resultant electric field produced will also be alternating at the same frequency.
A power cord connecting an appliance to an outlet will have an electric field surrounding it whether the appliance is tuned on or off (presence of electric potential is all that is needed). However a magnetic field will only be present around the cord if the appliance is turned on (electric current must flow).
Unlike magneticfields, the electricfields can be felt if strong enough (largerthan 40 kiloVolt per meter). Electric fields can also be shielded much easier. A grounded conductive mesh or screen surrounding the source of electriclield (a VDT for example) can eliminate it
A similar screen surrounding the object to be protected is just as effective. This is also known as the Faraday cage (Faraday - a well known scientist famous for his work in electromagnetism). The electric fields are easily disturbed (or distorted) by presence of conductive objects and the human body.
Most Electrical/Electronic devices emit Electromagnetic Fields. These include electric generating and transmission equipment such as utility power lines and transformer stations.
In the home they include almost all electrically operated appliances such as the TV, HI-Fl, MICROWAVE, STOVE/OVEN, VACUUM CLEANER, CLOCK-RADIO, ELECTRIC BLANKET, etc. In the office they include The COMPUTER and the VIDEO DISPLAY TERMINAL (VDT), PRINTERS, COPIERS, FAX, LIGHTING etc. And in the factory, all electrically operated TOOLS, OVENS, WELDING EQUIPMENT, etc.
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