Electronics - ELECTRONICS Current(I Current is the quantity...

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ELECTRONICS. Current (I) Current is the quantity of electrons passing a given point. The unit of current is the Ampere. One Ampere is 6,280,000,000,000,000,000 electrons passing a point in one second. Electrical current flows from a region of high charge or potential to a region of low potential. To make confusion worse there exist two notions about the direction in which current flows: Conventional Current assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source. This was the convention chosen during the discovery of electricity. They were wrong! Electron Flow is what actually happens and electrons flow out of the negative terminal, through the circuit and into the positive terminal of the source. However, the concept of Conventional Current is still applied to almost all the circuit schematics today, so we will use it extensively in this class. Voltage (V or E) Voltage is electrical pressure or force. Voltage is sometimes referred to as Potential. Voltage Drop is the difference in Voltage between the two ends of a conductor through which current is flowing. Power (P) The work performed by an electrical current is called Power. The unit of Power is the Watt. Resistance (R) Conductors are not perfect. They resist to some degree the flow of current. The unit of resistance is the Ohm. Load The part of the circuit which performs work (e.g. a motor, a light bulb or a LED, etc.) is called Load. Ohm's Law A set of rules that show the relationships among Current, Voltage, Power and Resistance. Given any two of the above, one is able to calculate the other two using the following formulas: E = I x R I = E / R R = E / I Winkler, Basics of Electricity/Electronics Workshop, p.1
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P = E x I Direct Current Electricity An electrical current can flow in either of two directions through a conductor. If it flows in only one direction whether steadily or in pulses, it is called direct current (DC). Almost all the projects in class will be powered by DC electricity. In order to be able to work with DC we need to convert the alternating current (AC) from the outlets into a direct current, which we use to power our circuits. A wall adapter transforms AC into DC, the wall adapter in our lab kit transforms 120 VAC into 9/12VDC. The maximum current it can provide is 1000mA (1A). The wall adapter has two wires that go to our circuits - one for positive power supply and one for negative (ground, or GND). Please also read chapters 2 and 3 in our course book “Physical Computing” (pp. 9 -48) in addition to following the following examples, descriptions and experiments: We take our power supply and cut off its plug - we want to replace it with a header that fits better in our prototyping boards. Solder the header to the power supply’s two wires as illustrated in the following picture. To prevent the solder joints from breaking put a blob of hot glue around them: Winkler, Basics of Electricity/Electronics Workshop, p.2
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Since direct current only flows in one direction, we have to be able to easily determine the positive and negative side of the power supply. Remember that we assume the
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