<text><span class="style10">lectro-magnetism</span><span class="style7"> </span><span class="style10">(1 of 5)</span><span class="style7">Electromagnetism is the study of effects caused by stationary and moving electric charges. Electricity and magnetism were originally observed separately, but in the 19th century, scientists began to investigate their interaction. This work resulted in a theory that electricity and magnetism were both manifestations of a single force, the electromagnetic force.The electromagnetic force is one of the fundamental forces of nature, the others being gravitational force and the strong and weak nuclear forces. Recently the electromagnetic and weak forces have been shown to be manifestations of an electro-weak force. Magnetism has been known about since ancient times, but it was not until the late 18th century that the electric force was identified - by the French physicist Charles Augustin de Coulomb (1736- 1806).</span><span class="style10">Magnetism</span><span class="style7">Metallic ores with magnetic properties were being used around 500 BC as compasses. It is now known that the Earth itself has magnetic properties Investigation of the properties of magnetic materials gave birth to the concept of </span><span class="style26">magnetic fields</span><span class="style7">, showing the force one magnet exerts on another. These lines of force can be demonstrated by means of small plotting compasses or iron filings (see diagram 1). An important feature of a magnet is that it has two poles, one of which is attracted to the Earth's magnetic north pole, while the other is attracted to the south pole. Conventionally, the north-seeking end of a magnet is called its </span><span class="style26">north pole</span><span class="style7">, and the other is the </span><span class="style26">south pole</span><span class="style7">. Magnets are identified by the fact that unlike or opposite poles (i.e. north and south) attract each other, while like poles (north and north, or south and south) repel each other.Magnetic effects are now known to be caused by moving electric charges. Atomic electrons are in motion, and thus all atoms exhibit magnetic fields.</span></text>
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<text><span class="style10">. The magnetic field</span><span class="style7"> around a bar magnet can be plotted using a small compass, or by scattering iron filings on a sheet of paper placed above it.</span></text>
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<layer>background</layer>
<id>23</id>
<text>ΓÇó STARS AND GALAXIESΓÇó QUANTUM THEORY AND RELATIVITYΓÇó WAVE THEORYΓÇó OPTICSΓÇó ELECTRICITY IN ACTIONΓÇó ATOMS AND SUBATOMIC PARTICLESΓÇó THE EARTH'S STRUCTUREΓÇó MEDICAL TECHNOLOGYΓÇó RADIO, TELEVISION AND VIDEOΓÇó SEEING THE INVISIBLE</text>
