metal conductor with an applied voltage The imparted force accelerates the

# Metal conductor with an applied voltage the imparted

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metal conductor with an applied voltage The imparted force accelerates the charges and superimposes an increased velocity onto the existing random motion of the charges SCI-122 Session 14 Electric Current: The nature of electrical current This resultant motion causes the charges to undergo a net drift toward one end of the conductor [positive charges moving from the (+) end of the voltage toward the ( ) end] SCI-122 Session 14 Electric Current: The nature of electrical current This is called the drift velocity of the current This drift velocity is on the order of about 0.01 cm/s

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9 SCI-122 Session 14 Electric Current: In summary An applied voltage will establish an electric field throughout a circuit at approximately the speed of light The field will impart a net motion to the loose charges in the circuit resulting in an electric current SCI-122 Session 14 Electric Current: In summary The average net drift velocity of the charges moving as a current is very slow while the field that moves them travels near the speed of light SCI-122 Session 14 Electric Current: Direction of charge movement Direct current (DC) Charges flow in only one direction Can be seen in electronic circuits Also seen in circuits that utilizes Chemical batteries Fuel cells Solar cells
10 Electric Current: Direction of charge movement Alternating current (AC) Charges alternately flow one way and then the other Can be seen in household circuits supplied by the electric utilities There is no net flow of charges from the outlets through the circuits The current changes direction 120 times per second in a household circuit (60 Hz) SCI-122 Session 13 Electric Resistance: The electric resistance (R) of a material depends on the following: Material (characterized by a quantity called resistivity, r) R Length R L SCI-122 Session 13 Electric Resistance: The electric resistance (R) of a material depends on the following: Cross-sectional area R 1/A Temperature R T

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11 Adding Resistances: In series L 1 L 2 L 3 + + L total = L 1 + L 2 + L 3 Since R L, as , L R Finally, R t = R 1 + R 2 + R 3 +… Adding Resistances: In parallel A 1 A 2 A 3 + + A total > A 1 or A 2 or A 3 A R Finally, = + + + … 1 1 1 1 R t R 1 R 2 R 3 1 A Since R , as , SCI-122 Session 14 Ohm’s Law: The affect of voltage on current As V I The affect of resistance on current As R I Ohm’s Law I V 1 R I V R I

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