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Electric Current and Circuits Direct Current Direct Current: A flow of charge that ALWAYS flows in one direction. A battery – The terminals are + and - . Electrons always move through the terminals in the same direction. They move from negative to positive. Ex. Alternating Current Electrons in the circuit move first in one direction and then in the opposite direction. (Alternating back & forth) This is done by alternating the “polarity” at the voltage source. Buildings including homes use alternating current at 120 volts Electric Current (I) Depends on voltage(V) and resistance(R) Current is measured in amps(A) Voltage is measured in volts(V) Resistance is measured in ohms(Ω) Ohm’s Law : describes the relationship between voltage, current and resistance V = IR Electric Power The rate at which electrical energy is converted to Mechanical energy, heat or light is Electric Power. The electrical energy comes from power stations that use electromechanical generators powered by heat engines fueled by burning coal, falling water, wind or nuclear power to make electricity. Formula to calculate POWER Electric Power = current x voltage UNITS-1 watt = 1 ampere x 1 volt Ex. Calculate how much power is used by a calculator that operates on 8 V and 0.1 A. Power = current x voltage P = (I) (V) P = (0.1A) (8V) P = 0.8 W Ex. Will a 1200-watt hair dryer operate on a 120-volt line if the current is limited to 15 amperes by a safety fuse? How many watts can the circuit provide? P = IV P = 15A x 120V P = 1800 watts YES ! It can run !! Electric Circuits There must be a complete path from the positive terminal of the battery to the negative terminal of the battery Any path along which electrons can flow is a circuit It must be continuous Two Types of circuits Series—from a single pathway for electron flow Parallel—from branches, each of which is a separate path for the flow of electrons Series Parallel Series circuit Single pathway for current to flow Current is resisted by each device and the sum is the total resistance of the pathway Current = voltage/resistance Total voltage divides among each device If one device fails, the circuit fails to function Parallel circuit Each device has its own pathway from one terminal to the other Voltage is same across each device Total current divides amongst the branches Total circuit is sum of the current in the branches As branches increases, resistance decreases Schematic diagrams Simple diagrams to describe electric circuits Zig zag line shows resistance and resistance free wires are solid lines