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Electric Current Introduction What would happen if you put a small positive charge between two plates? + + + + + + + + + + + + + + + + + + + + + + + + + E – – – – – – – – – – E – – – – – high potential (high energy per charge) – – – – – – – – – low potential What if you just connected the two plates with a metal wire? + + + E + + + + + + + + + + + + + + + current q I t – – – – – – – – – – + + + + + high potential (high energy per charge) + charge will flow from high potential to low potential until plates are neutralized. – – + – – – – – – – – – – – – low potential Electric Current q I t • The rate of flow of electric charge. • Measured in C/s or Amps (A). • Conventional current is defined to be the direction of flow of positive charge. How could you make the flow of current constant? + + + + + + + + + + + + + + + + + + + + + E + + + high potential (high energy per charge) DO WORK! – – – – – – – – – – – – – – – – – – – – – – – – low potential Vocabulary • Voltage (V) – aka electric potential difference [Volts – V] • Current (I) – rate of flow of charge [Amps – A] – Direct current (dc) – same direction all times – Alternating current (ac) – changes direction • Resistance (R) – how much the flow of charge restricted [Ohms – Ω] L R A ρ = resistivity [Ω∙m] L = length [m] A = area [m2] Copper has a very low resistance which is why it is often used for wiring. What is the relationship between voltage, current, and resistance? • Use what you know about finding mathematical relationships to find “Ohm’s Law” with a rheostat. V IR Power U e qV q P V IV t t t P IV 2 V P IV I R R 2