1. Direct Current (DC) and Alternating Current (AC). Series Circuits and Parallel Circuits.

2. 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.

3. 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).

4. 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.

5. AC in the USA In the US, current changes direction 120 times per second, for a frequency of 60 cycles per second or 60 Hertz. Normal outlet voltage in the US is 110-120 volts, although some large household appliances run on 220-240 volts.

6. 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. A capacitor produces a retarding effect on charges in current flow.

7. 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

8. 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

10. 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. Current in the circuit will go down (lights will dim) If you remove a light bulb or one burns out—all go out!

11. Current, Voltage, and Resistance in Series

12. 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

13. Parallel Circuits Place two bulbs in parallel. What do you notice about the brightness of the bulbs? Add a third light bulb in the circuit. What do you notice about the brightness of the bulbs? Remove the middle bulb from the circuit. What happened?

14. 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.

15. 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

16. 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.