Rabu, 16 Maret 2011

Moving Charges And Magnetic Fields

Moving Charges And Magnetic Fields

You can see the shape of the magnetic field established by the current by running a straight wire vertically through a sheet of paper. The wire is connected to a battery, and iron filings are sprinkled on the paper. The filings will become aligned as each tiny piece of iron is moved parallel to the field. Overall, filings near the wire form a pattern of circles with the wire in the center.

A current-carrying wire that is formed into a loop has circular magnetic field lines that pass through the inside of the loop in the same direction. This has the effect of concentrating the field lines, which increases the magnetic field intensity. Since the field lines all pass through the loop in the same direction, one side of the loop will have a north pole and the other side a south pole.

Many loops of wire formed into a cylindrical coil are called a solenoid. When a current passes through the loops of wired in a solenoid, each loop contributes field lines along the length of the cylinder. The overall effect is a magnetic field around the solenoid that acts just like the magnetic field of a bar magnet. This electromagnet can be turned on or off. In addition, the strength of the electromagnet depends on the size of the current and the number of loops. The strength of the electromagnet can also be increased by placing a piece of soft iron in the coil.

A solenoid can serve as an electrical switch or valve. It can be used as a water valve by placing a spring-loaded movable piece of iron inside the wire coil. When a current flows in such a coil the iron is pulled into the coil by the magnetic field, turning the hot or cold water on in a washing machine or dishwasher, for example. Solenoids are also used as mechanical switches on VCR's automobile starters, and signaling devices such as door bells and buzzers.

Read more: http://www.articlesbase.com/tutoring-articles/moving-charges-and-magnetic-fields-4423573.html#ixzz1GpwH7Wrf
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