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Direct Current (DC) and Alternating Current (AC). Series Circuits and Parallel Circuits. Direct Current (DC) • Direct Current is a flow of charge that always flows in one direction • A DC current is a current that does not change direction in time. • A battery produces direct current in a circuit. Example: Portable flashlight circuit. Alternating Current (AC) • An Alternating Current (AC) current is a current that changes direction in time. • If the high & low voltage terminals switch locations periodically, the current will flow back and forth in the circuit. This is called alternating current (AC). Alternating Current • In alternating current (AC) electrons in a circuit move in one directions and then in opposite direction, alternating back and forth about relatively fixed position. • Alternating current is accomplished by alternating polarity voltage at the generator or other voltage source. • AC current flows in your home. AC in the USA • In public power distribution systems in the United States, (including household current), the voltage reverses itself 60 times per second. In some countries, the voltage reverses itself 50 times per second. • Normal outlet voltage in the US is 110-120 volts, although some large household appliances run on 220-240 volts. Converting AC and DC • The current in your home is AC. The current in a battery operated device is DC. AC is converted to DC using devices called diodes, which allow charges to move in only 1 direction. • Diode is a tiny electronic device that acts a one way valve to allow electron flow in only one direction. • Because alternating current vibrate in two directions , only half of each cycle will pass through a diode. A capacitor is used to have continuous current. Series and Parallel Circuits • Series Circuits: only one end of each component is connected Example: Christmas tree lights • Parallel Circuits: both ends of a component are connected Example: household lighting Series Circuits Series circuit: • All in a row • Current has one path for electrons • Current flows through every part of the circuit • 1 light goes out and the circuit is broken Adding Resistor to Series • If you add a resistor (like another light): • Total resistance goes up since all the current has to go through each resistor. • If you remove a light bulb or one burns out—all go out! Current, Voltage, and Resistance in Series • Current is the same at all points • Use Ohm’s Law to find current using resistance and voltage • I= 𝑉 𝑅 • Voltage is reduced by each resistance – voltage drop • Add up all resistors to get total • Total resistance will go up because all of the current must go through each resistor. Parallel Circuits Parallel circuit: • More than one path for current to flow • Paths are also known as branches • Has at least one point where current divides • 1 light goes out and the others stay on Parallel Circuits • If you add a resistor: –Total resistance goes down –Total current goes up when you add another path • If you remove a light bulb or one burns out, the others stay on because the circuit is still closed. Current and Voltage in Parallel Circuits • Current flows into a branching point, the same total current must flow out again • Current depends on resistance in each branch • Voltage is the same across each branch – because each branch is on the same wire Series and Parallel Circuits • Series Circuit: Current is the same at all points in the circuit. • Parallel Circuit: Current is shared between the components • Adding resistor in series increases resistance and slows the current flow. • Adding resistor in parallel lowers resistance and increases the current flow.