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MODULE V - FUNDAMENTALS OF ELECTRONICS
What is current? A flow of electrons forced into motion by voltage is known as current. Inside a copper wire, current is carried by small negatively-charged particles, called electrons. The electrons drift in random directions until a current starts to flow. When this happens, electrons start to move in the same direction. The size of the current depends on the number of electrons passing per second. When an emf (voltage) is impressed across a conductor it drives these free electrons away from the negative force toward the positive. This action takes place at near the speed of light, 300,000,000 metres per second although individual electrons do not move far they have a shunting effect. This is similar to a number of cars pulled up at traffic lights when the last vehicle fails to stop and hits the second last vehicle which in turn hits the third last vehicle... The amount of current in a circuit is measured in amperes (amps). Smaller units used in electronics are milli-amps mA (1 / 1,000th of an ampere) and micro-amps uA (1 / 1,000,000th of an ampere). An ampere is the number of electrons going past a certain point in one second. |   |
The quantity of electrons used in determining an ampere is called "coulomb" which one ampere is one coulomb per second. A coulomb is 6,280,000,000,000,000,000 or 6.28 X 10 18 electrons.
This is the unit of measuring electrical quantity or charge. Current is represented by the symbol I, and is measured in amperes, or 'amps', A. One ampere is a flow of 6.24 x 1018 electrons per second past any point in a wire. That's more than six million million million electrons passing per second. This is a lot of electrons, but electrons are very small and each carries a very tiny charge. In electronic circuits, currents are most often measured in milliamps, mA, that is, thousandths of an amp. |
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