1. Electric Circuits 4/27/15

2. Key Terms  Charge (q): The fundamental property of attraction / repulsion of electrons and protons. Unit is coulomb (C)  Current (I): The flow of electrical charge. Unit is amperes (A)

3. Key Terms  Voltage (V): The electric potential energy of a circuit. Unit is volts (V)  Conservation of Charge: The net electric charge is neither created or destroyed but can be transferred

4. Key Terms  Resistance (R): The difficulty of a charges to flow through a circuit element. Unit is Ohms (Ω)  Resistivity (ρ): A property of a material that allows or impedes the flow of charge. Unit is Ohm meter (Ωm)

5. Key Terms  Conductors: A material (like metal) through which electric charge can flow  Insulators: A material where electric cannot flow freely

6. Key Terms  Series Circuit: Resistors connected in a single path  Parallel Circuit: Resistors are connected to the same two points of a circuit, so that any single resistor completes the circuit independently

7. Conditions for a Circuit  There must be a closed conducting path that extends from the positive terminal to the negative terminal.  There must be an electric potential difference across the two ends of the circuit.

8. Voltage Sources  Do work on each charge it encounters  Which transfers into electric potential energy

9. The Battery  A negative charge will gain potential energy and voltage as it moves from positive terminal to negative terminal in the battery

10. The Circuit  A negative charge will lose potential energy and voltage as it moves from negative terminal to positive terminal in the circuit

11. Battery and Circuits  A negative charge has the least amount potential energy at positive terminal  A negative charge has the greatest amount potential energy at negative terminal Voltage = Potential Difference High PE Low PE

12. Ohm’s Law  Ohm's law: states that the current through a conductor between two points is directly proportional to the potential difference across the two points (linear relationship)

13. Ohm’s Law

14. Current as a Water Slide  Voltage source = The water pump  Voltage (voltage difference) = Height of the slide  Positive terminal = Bottom of the slide  Negative terminal = Top of the slide

15. Current as a Water Slide  Current = Rate at which water is flowing  Charge = The water  Resistors (electric device) = The pool  On/Off Button = Power switch

17. Waterslide vs. Circuit

18. Kirchoff Junction Rule  At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node  i 2 + i 3 = i 1 + i 4

19. Kirchoff Loop Rule  The directed sum of the electrical potential differences (voltage) around any closed network is zero  The energy of circuit has to obey the conservation of energy

20. Kirchoff Loop Rule v1 + v2 + v3 - v4 = 0

21. Voltage Source Examples

22. Voltage Sources Examples  Ex 1) Low voltage and low current  D-Cell battery: 1.5 V and 0.1 A  Low waterfall with only trickle of water flowing

23. Voltage Sources Examples  Ex 2) High voltage and high current  Power lines: 50,000 volts and 65 A  High waterfall with a river of water flowing over it

24. Voltage Sources Examples  Ex 3) High voltage and low current:  Electric fence: 6000 V and 0.1 A  High waterfall with only trickle of water flowing

25. Voltage Sources Examples  Ex 4) Low voltage and high current:  Car battery: 12 V and 30 A  Low waterfall with a gushing river of water flowing

26. True or False Revisited 1. When a battery no longer works, it is out of charge. 2. A battery can be a source of charge in a circuit. The charge which flows through the circuit originates in the battery. 3. Charge becomes used up as it flows through a circuit. The amount of charge which exits a light bulb is less than the amount which enters the light bulb.

27. True or False Revisited 4. Charge flows through circuits at very high speeds. This explains why the light bulb turns on immediately after the wall switch is flipped. 5. The local electrical utility company supplies millions and millions of electrons to our homes everyday. 6. High voltage circuit means there is a large current.

28. Quiz Tomorrow  Electrostatic WS  Circuit WS (#1-3)

30. Ohm’s Law  Ohm's law: states that the current through a conductor between two points is directly proportional to the potential difference across the two points (linear relationship)

31. Ohm’s Law

32. Circuit Equations  I = Δq / Δt (Electric Current)  R = ρ l / A (Electric Resistance)  I = ΔV / R (Ohm’s Law)  P = I ΔV (Electric Power)

33. Kirchoff Junction Rule  At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node  i 2 + i 3 = i 1 + i 4

34. Kirchoff Loop Rule  The directed sum of the electrical potential differences (voltage) around any closed network is zero  The energy of circuit has to obey the conservation of energy

35. v1 + v2 + v3 - v4 = 0

37. Schematic Symbols Wires: Resistor (elec. device): Switch: Battery: Fuse: Connected wires: Unconnected wires

38. Schematic Symbols Wires: Resistor (elec. device): Switch: Battery (Outlet): Fuse: Connected wires: Unconnected wires