1. Series and Parallel Circuits 1 Lesson 9 November 17 th, 2010

2. Designing Circuits The simplest circuit is a loop, but this isn’t always the best design when there are a variety of different components in the circuit. Designers have to ensure that one component does not depend on another.

3. Designing Circuits In more complex devices there are multiple electrical loops, if one loop breaks the others will continue to function properly.

4. Tiny Circuits Conventional switches and other electrical components are practical and convenient for homes or simple, large electrical devices. Miniature circuits in advanced electronic devices require transistors instead. A transistor is a tiny device that acts as a switch or amplifier in a circuit. ◦ Often referred to as solid-state components because they are made of solid material with no moving parts.

5. Tiny Circuits Made of three layers of specially treated silicon. The middle layer controls a current between the outer layers which allows them to work as switches.

6. Tiny Circuits Microcircuits (integrated circuits) are made up of microscopic transistors and other electrical devices. ◦ A circuit on an extremely small scale. Microcircuits regularly contain more than a million components per square centimetre

7. Circuit Diagrams Engineers and designers of electrical circuits use special symbols that show the components and connections in a circuit. A drawing made with these symbols is called a circuit diagram.

8. Circuit Diagrams Follow these rules when you draw circuit diagrams. 1. Always use a ruler to draw straight lines for the conducting wires. 2. Make right-angle corners so that your finished diagram is a rectangle.

9. Electric Circuit Diagrams and Symbols Conductor or wire ◦ To pass current very easily from one part of a circuit to another.

10. Electric Circuit Diagrams and Symbols Cell-Supplies electrical energy ◦ The positive end is bigger than the negative end.

11. Electric Circuit Diagrams and Symbols 2 Cells Note: every time a cell is added you need to draw another cell.

12. Electric Circuit Diagrams and Symbols DC Source- Electrical energy source ◦ DC = Direct current, always flows one way

13. Electric Circuit Diagrams and Symbols AC Source - Electrical energy source AC = Alternating current, continually changing direction

14. Electric Circuit Diagrams and Symbols Ground – ◦ A connection to earth

15. Electric Circuit Diagrams and Symbols Switch - An on-off switch allows current to flow only when it is in the closed (on) position

16. Electric Circuit Diagrams and Symbols Lamp ◦ A transducer which converts electrical energy to light

17. Electric Circuit Diagrams and Symbols Resistor ◦ A resistor restricts the flow of current,

18. Electric Circuit Diagrams and Symbols Ammeter ◦ -Device that measures current A

19. Electric Circuit Diagrams and Symbols Voltmeter -Device that measures voltage V

20. Electric Circuit Diagrams and Symbols Motor -electrical load that converts electrical energy into movement M

21. Series Circuits Electric circuit in which the components are arranged one after another in series. A series circuit has only one path along which electrons can flow.  If that pathway is interrupted, the whole circuit cannot function.

22. Series Circuits The amount of current is the same in all parts of a series circuit. If more resistors are added, it will increase the total resistance of the circuit.  This decreases the current.

23. Series Circuits Example: Adding an extra bulb to a series string of lights makes all the bulbs dimmer. Electrons use up all their potential difference going around a series circuit no matter how many loads are in the circuit. Each load will use part of the total potential difference, depending on how much it resists the flow of electrons.

24. Parallel Circuits A parallel circuit is an electric circuit in which the parts are arranged so that electrons can flow along more than one path. The points where a circuit divides into different paths or where paths combine are called junction points An interruption or break in one pathway does not affect the other pathways in the circuit.

25. Parallel Circuits Similarly, adding a new pathway with more resistors does not affect the resistance in any of the other pathways. Adding extra resistors in parallel decreases the total resistance of the circuit.

26. Parallel Circuits Each electron has the same amount of energy, and electrons must expend all their energy on the path they are on. This is why the potential difference across parallel resistors will always be the same, even though the resistors themselves are of different values

27. Loads connected in parallel circuits have different currents

28. Summary of Current, potential difference, and resistance in series and parallel circuits. CircuitPotential Difference Series circuit Each load uses a portion of the total potential differences supplies by the battery Parallel circuit Each load uses all the potential difference supplied by the battery.

29. Summary of Current, potential difference, and resistance in series and parallel circuits. Circuit Current Series circuit The current is the same throughout a series circuit Parallel circuit The current divides into different paths. A pathway with less resistance will have a greater current

30. Summary of Current, potential difference, and resistance in series and parallel circuits. Circuit Resistance Series circuit The current decreases when more resistors are added Parallel circuit Adding resistors in parallel decreases the total resistance of the circuit.

31. Two Types of Circuits Combined Series circuits and parallel circuits make up the circuits in your home and school.

32. Two Types of Circuits Combined Some circuits are combinations of series circuits and parallel circuits. These combinations help prevent problems such as the all the lights in the house going out because one bulb burnt out.

33. It is also an important safety feature in a combination circuit to have some switches wired in series, because it is sometimes necessary to turn off the electricity in part or all of a home

34. Questions U3 L9 Draw a circuit diagram for a circuit that includes a resistor, a switch, conducting wires, and a battery. C (1) Draw a circuit diagram of a series circuit with a battery, connecting wires, and one light bulb. C (1) Draw a circuit diagram of a parallel circuit with a battery, connecting wires and two light bulbs. C (1) What happens to the voltage in a series circuit when more loads are added? I (1) What happens to the current in a parallel circuit when more loads are added? I (1) How do combination circuits help prevent problems in circuits in a home? I (1)