If a charge is placed at rest at a point near a metallic wire carrying current, it experiences almost no force. From this, we conclude that there is no appreciable electric field at that point. The wire is electrically neutral and does not produce an electric field.
However if the charge is projected from the point, in the direction of the current, it is deflected towards the wire. There must be a field at that point which exerts a force on the charge when it is projected, but not when it is kept at rest. This field is different from the electric field which exerts a force on a charged particle whether it is at rest or in motion. This phenomenon is called MAGNETISM and this new field is called the magnetic field. The force exerted by the magnetic field is called magnetic force.
Or in simpler words, magnetism is the force that acts between certain objects at a distance or when they are touching. The direction of the magnetic field at the centre of a circular wire can be obtained using the right hand thumb rule. If the fingers are curled along the current, the stretched thumb will point towards the magnetic field. Another way to find the direction, is to look into the loop along its axis. If the current is in anticlockwise direction, the magnetic field is towards the viewer. If the current is in clockwise direction, the field is away from the viewer.
There are two types of magnets-permanent magnets and electromagnets. An ordinary bar magnet will pick up and support nails or other bits of iron and steel. Its magnetism is strongest at its ends (its poles). If a piece of iron or steel is stroked in one direction with the bar magnet, the piece becomes a magnet too. An electromagnet can be made by winding a coil or wire around a bar of iron and passing an electric current through the wire. The strength of the magnet increases with the number of turns in the coil and with the strength of the electric current. Two wires carrying electric currents in the same direction will attract each other magnetically. Electromagnets can be made more powerful than ordinary magnets and are used around the home in Television sets, tape recorders, telephones, as well as in huge industrial motors.
William Gilbert was the first to use the terms magnetic pole and electric force, and suggested that the Earth’s magnetism could be explained if the earth were compared to a huge bar magnet. He thought (wrongly) that the planets held their orbits around the Sun by magnetic forces.
cheap real viagra