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Basic Electronics Engineering I |
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| :: Current |
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Free electrons are available in all conductive and semi conductive materials. These electrons drift randomly in all directions within the material, When a voltage is applied across the material, electrons start flowing from the negative to the positive side. Voltage is the driving force that causes a charge to flow. The free electrons in motion provide an electric current, symbolized by |
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Current is measured by the number of electrons (having a charge, Q) that flow through the specific area per unit of time t. The unit of current is the ampere, A. One ampere of current results when one coulomb of charge passes through the given area in one second. The current indicates the intensity of the charge in motion. With no voltage applied, there is no current. With more applied voltage, a larger amount of charge will pass a given point, which means a higher current. |
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When a current is present, the free electrons move through the material and occasionally collide with atoms. Because of these collisions, electrons lose some energy and their movement is restricted.
The property of the material that restricts the flow of current is called resistance, r. The unit of resistance is the ohm, symbolized by the Greek letter omega  . Resistance is the opposition to current. Conductors have very little resistance; insulators have high resistance value. |
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