1. Agenda Today –Finish Chapter 25 –Cover Resistors in DC circuits Tues Lab & Quiz on Ch. 24-25 Finish 26 this week then…. –Freedom?

2. Circuit Current made up of “+” charges Call them “holes” R1R1 I + - “+” charges s exit + terminal Flow through circuit Return to “-” terminal Need return path for current flow

3. Circuit Current made up of “+” charges Call them “holes” R1R1 I + - “+” charges s exit + terminal Flow through circuit Return to “-” terminal Need return path for current flow What happens here? - +

4. Circuit Current made up of “+” charges Call them “holes” R1R1 I + - “+” charges s exit + terminal Flow through circuit Return to “-” terminal Call “-” zero volts as reference here 0 V Indicates “ground” reference

5. Voltage in a given area R1R1 I + - 0 V A B C D E F AB Distance V 0 1.5V

6. Voltage in a given area R1R1 I + - 0 V A B C D E F AB Distance V 0 1.5V Voltage Constant in a wire!

7. Voltage in a given area R1R1 I + - 0 V A B C D E F BC Distance V 0 1.5V Voltage in resistor?

8. Voltage in a given area R1R1 I + - 0 V A B C D E F BC Distance V 0 1.5V Voltage in resistor? Not constant: Why linear? Resistance increases with length…. R=  L/A

9. Voltage in a given area R1R1 I + - 0 V A B C D E F CD Distance V 0 1.5V Voltage in ?

10. Voltage in a given area R1R1 I + - 0 V A B C D E F CD Distance V 0 1.5V Voltage in ? Wire: ~ constant

11. Voltage in a given area R1R1 I + - 0 V A B C D E F CE Distance V 0 1.5V Voltage in ? Wire: ~ constant D

12. Voltage in a given area R1R1 I + - 0 V A B C D E F C E Distance V 0 1.5V Voltage in ? Wire: ~ constant DF

13. Voltage in a given area R1R1 I + - 0 V A B C D E F FA Distance V 0 1.5V Voltage in Battery? Voltage Source?

14. Voltage in a given area R1R1 I + - 0 V A B C D E F FA Distance V 0 1.5V Voltage in increases from “-” to “+” Nor clear internal workings No matter, just worry about terminal areas

15. Voltage in a given area R1R1 I + - 0 V A B C D E F A B Distance V 0 1.5V Complete Circuit Voltage ends where it began… (Loop) C F A

16. Voltage Loop Math I + - 0 V A B C D E F V A – V A = 0 V AA = V A – V A V AB = V A – V B V AA = V AB + V BC + V CD + V DE + V EF + V FA = 0 V AA = 0 + 1.5V + 0V + 0 V + 0V + (-1.5V) = 0 Useful trick Find any loop in a circuit Voltage around entire loop must be zero Powerful…. 1.5 V Battery

17. Back to Energy Power = Watts (W) Power = J/s [Energy per second] Volts = J/C Energy = V x C Power = Energy / time = V x C/s Power = IV

18. Electricity Equations Big 2! V = IR P = IV Mix & Match P=I 2 R, P=V 2 /r, etc…

19. Energy Conservation Energy in = Energy Out Power in = Power Out I + - 0 V A B E F Power into Circuit: From Battery Power Out of Circuit: Resistor R’s Convert Electricity to Heat, light, etc,,, Toaster?

20. Charge Conservation Charge in = Charge Out Current in = Current Out I + - 0 V A B E F Current into Circuit: From Battery Current flowing through : Resistor, Wires I BAT = I WIRE = I R No other way to go!

21. Resistor Combinations Wish to discover “total” or equivalent resistance for a combination of multiple Resistors Most circuits have >1 component… Insight into output of power source Useful first step in determining circuit properties Resistors useful –Control V & I –Create light & heat –Protection of sensitive components Examine logic, conservation laws, math, observations

22. Water tower Water Tower Potential Energy from Gravity PE = mgh Forces water down [pressure] Which Allows the most water to flow per minute? A: Both Connected

23. Water tower Water Tower Potential Energy from Gravity PE = mgh Forces water down [pressure] Which Allows the most water to flow per minute? B: Only Left Connected

24. Water tower Water Tower Potential Energy from Gravity PE = mgh Forces water down [pressure] Which Allows the most water to flow per minute? C: Only Right Connected

25. Water tower Water Tower Potential Energy from Gravity PE = mgh Forces water down [pressure] Which Allows the most water to flow per minute? Addition of multiple hoses to same starting point increases flow & Decreases Resistance A: Both Connected

26. Water tower Water Tower Potential Energy from Gravity PE = mgh Forces water down [pressure] Addition of multiple hoses to same starting point increases flow & Decreases Resistance What if we added a third? Fat or skinny? Would flow ever decrease? A: Both Connected

27. Water tower Water Tower Potential Energy from Gravity PE = mgh Forces water down [pressure] Rule one of hoses (& resistors): Multiple pathways reduce resistance “Parallel” Connections

28. Water tower Water Tower Potential Energy from Gravity PE = mgh Forces water down [pressure] Compare  PE for water falling through the two hoses… Same for both Examine electrical circuit

29. Parallel Circuit I + - A B E C F G Top of Tower Drain Compare Voltages at A,B,C

30. Parallel Circuit I + - A B E C F G Top of Tower Drain Compare Voltages at E,F,G

31. Parallel Circuit I + - A B E C F G Top of Tower Drain Compare Voltages across Battery & R’s Does the size of each R matter?

32. Parallel Circuit I + - A B E C F G Top of Tower Drain Compare Voltages across Battery & R’s Does the current have to be the same?

33. Parallel Circuit I + - A B E C F G Top of Tower Drain Compare Voltages across Battery & R’s Does the current have to be the same?

34. Parallel Circuit Rules Voltage same across parallel components Current Can be Different Each additional component reduces total resistance Derive this for three resistors? –Turn in for extra credit on quiz tomorrow…

35. Water tower Water Tower Which Allows the most water to flow per minute? A: Both Connected

36. Water tower Water Tower Which Allows the most water to flow per minute? B: Thick one?

37. Water tower Water Tower Which Allows the most water to flow per minute? C: Just Skinny?

38. Water tower Water Tower Which Allows the least water to flow per minute? A: Both Connected

39. Water tower Water Tower Addition of multiple hoses in line decreases flow & Iecreases Resistance What if we added a third? Fat or skinny? Would flow ever increase?

40. Water tower Water Tower Another Rule of hoses: (resistors?) Addition of more hoses in line (“Series”) always Increases resistance

41. Water tower Water Tower Compare flow of water through each pipe … Same for both: What leaves one must enter the other…. Examine electrical circuit

42. Series Circuit I + - A B D C Top of Tower Drain Compare Voltages at A,B,C, D E R1 R2

43. Series Circuit I + - A B D C Top of Tower Drain Compare Voltages across R1 & R2 vs. Battery E R1 R2

44. Series Circuit I + - A B D C Top of Tower Drain Compare Current from Battery & through R’s R1 R2 E

45. Series Circuit Rules Current same along components in series Voltage Can be Different Each additional component increases total resistance Derive this for three resistors? –Turn in for extra credit on quiz tomorrow…

46. Parallel Circuit Rules Voltage same across parallel components Current Can be Different Each additional component reduces total resistance Derive this for three resistors? –Turn in for extra credit on quiz tomorrow…

47. Agenda Today –Finish Chapter 25 Monday –Simple Circuitry (ch. 26) Tues Lab & Quiz on Ch. 24-25 Wed: Solve Resistor Circuits Fri: Capacitors in DC circuits…. –Freedom? Summer / Other Res. Interest…