1. Electrical Current (5) There are electrical currents in your phone, in your house, and in the hearts of your loved ones. Mr. Klapholz Shaker Heights High School

2. The basic quantities: Charge Current Potential Difference (“Voltage”) Resistance

3. Charge (1 of 2) Charge can be _ _ _ _ _ _ _ _ or negative. Symbol: Q or q. Units: Coulomb (C) Like charges _ _ _ _ _. Opposite charges _ _ _ _ _ _ _. An object will be neutral if it has _ _ _ _ _ numbers of positive and negative charges.

4. Charge (1 of 2) Charge can be positive or negative. Symbol: Q or q. Units: Coulomb (C) Like charges _ _ _ _ _. Opposite charges _ _ _ _ _ _ _. An object will be neutral if it has _ _ _ _ _ numbers of positive and negative charges.

5. Charge (1 of 2) Charge can be positive or negative. Symbol: Q or q. Units: Coulomb (C) Like charges repel. Opposite charges _ _ _ _ _ _ _. An object will be neutral if it has _ _ _ _ _ numbers of positive and negative charges.

6. Charge (1 of 2) Charge can be positive or negative. Symbol: Q or q. Units: Coulomb (C) Like charges repel. Opposite charges attract. An object will be neutral if it has _ _ _ _ _ numbers of positive and negative charges.

7. Charge (1 of 2) Charge can be positive or negative. Symbol: Q or q. Units: Coulomb (C) Like charges repel. Opposite charges attract. An object will be neutral if it has equal numbers of positive and negative charges.

8. Charge (2 of 2) If like charges are near each other, there is a _ _ _ of electrical potential energy. [Example: lightning.] If unlike charges are far from each other, there is a _ _ _ of electrical potential energy. [Example: charging a rechargeable battery.] The charge on an electron is - 1.602 x 10 -19 C. The charge on a proton is C. There are 6.25 x 10 18 C protons in 1 C.

9. Charge (2 of 2) If like charges are near each other, there is a lot of electrical potential energy. [Example: lightning.] If unlike charges are far from each other, there is a _ _ _ of electrical potential energy. [Example: charging a rechargeable battery.] The charge on an electron is - 1.602 x 10 -19 C. The charge on a proton is _______________ C. There are 6.25 x 10 18 C protons in 1 C.

10. Charge (2 of 2) If like charges are near each other, there is a lot of electrical potential energy. [Example: lightning.] If unlike charges are far from each other, there is a lot of electrical potential energy. [Example: charging a rechargeable battery.] The charge on an electron is - 1.602 x 10 -19 C. The charge on a proton is ______________ C. There are 6.25 x 10 18 C protons in 1 C.

11. Charge (2 of 2) If like charges are near each other, there is a lot of electrical potential energy. [Example: lightning.] If unlike charges are far from each other, there is a lot of electrical potential energy. [Example: charging a rechargeable battery.] The charge on an electron is - 1.602 x 10 -19 C. The charge on a proton is +1.602 x 10 -19 C. There are 6.25 x 10 18 C protons in 1 C.

12. Current Current is the rate at which charge flows. Symbol: I or i. I = Q / T Units: Ampere (A) 1 Amp = 1 _ _ _ _ _ _ _ / _ _ _ _ _ _. Surprisingly, in the International System the Amp is a fundamental unit: m k s A. An object with a current passing through it does not gain charge: just as much charge leaves as arrives.

13. Current Current is the rate at which charge flows. Symbol: I or i. I = Q / T Units: Ampere (A) 1 Amp = 1 Coulomb/second. Surprisingly, in the International System the Amp is a fundamental unit: m k s A. An object with a current passing through it does not gain charge: just as much charge leaves as arrives.

14. Potential Difference (“Voltage”) This is the single most abstract idea in the physics curriculum. Roughly speaking, potential difference is the energy per charge. More exactly, potential difference is the electrical potential energy difference per charge. Symbol: V V =  E / Q. Units: Volts (V). 1 Volt = 1 _ _ _ _ _ / _ _ _ _ _ _ _. Voltage causes current.

15. Potential Difference (“Voltage”) This is the single most abstract idea in the physics curriculum. Roughly speaking, potential difference is the energy per charge. More exactly, potential difference is the electrical potential energy difference per charge. Symbol: V V =  E / Q. Units: Volts (V). 1 Volt = 1 Joule / Coulomb. Voltage causes current.

16. Electrical Potential Energy Electrons flow away from the negative place, and toward the positive place. Protons have a force on them too. Protons are forced away from positive charge and toward negative charge. Positive locations have high PE, and negative locations have low PE. If current were made of positive charges, then in a circuit they would flow from the positive end of a battery, through wires, to the negative end of the battery. Electrons flow the other way.

17. Resistance (1 of 2) This is a measure of how tough it is to make charge flow through an object. Symbol: R Units: _ _ _ (  ) Long object have a _ _ _ of resistance. Narrow objects have a _ _ _ of resistance. Ceramics have a _ _ _ of resistance. Metals do _ _ _ have much resistance.

18. Resistance (1 of 2) This is a measure of how tough it is to make charge flow through an object. Symbol: R Units: Ohm (  ) Long object have a _ _ _ of resistance. Narrow objects have a _ _ _ of resistance. Ceramics have a _ _ _ of resistance. Metals do _ _ _ have much resistance.

19. Resistance (1 of 2) This is a measure of how tough it is to make charge flow through an object. Symbol: R Units: Ohm (  ) Long object have a lot of resistance. Narrow objects have a _ _ _ of resistance. Ceramics have a _ _ _ of resistance. Metals do _ _ _ have much resistance.

20. Resistance (1 of 2) This is a measure of how tough it is to make charge flow through an object. Symbol: R Units: Ohm (  ) Long object have a lot of resistance. Narrow objects have a lot of resistance. Ceramics have a _ _ _ of resistance. Metals do _ _ _ have much resistance.

21. Resistance (1 of 2) This is a measure of how tough it is to make charge flow through an object. Symbol: R Units: Ohm (  ) Long object have a lot of resistance. Narrow objects have a lot of resistance. Ceramics have a lot of resistance. Metals do _ _ _ have much resistance.

22. Resistance (1 of 2) This is a measure of how tough it is to make charge flow through an object. Symbol: R Units: Ohm (  ) Long object have a lot of resistance. Narrow objects have a lot of resistance. Ceramics have a lot of resistance. Metals do not have much resistance.

23. Resistance (2 of 2) When a potential difference is put across a wire, the electrons move toward the positive end. This is a current. While flowing, electrons slam into the particles in the solid; this _ _ _ _ _ the electrons; their motion is resisted. The current is limited.

24. Resistance (2 of 2) When a potential difference is put across a wire, the electrons move toward the positive end. This is a current. While flowing, electrons slam into the particles in the solid; this slows the electrons; their motion is resisted. The current is limited.

25. The essential hardware: Wire Bulb Cell and Battery Resistor Circuit

26. Wire Wires are conductors. Wires do not have a lot of resistance.

27. Insulators Insulators have high resistance. Why are the insulators in the photo just as vital as the conductors?

28. Bulb The filament is a resistor. Why does it glow?

29. Battery Inside a battery are chemicals ‘cells’. The reaction pushes electrons toward the negative pole. The reaction pulls electrons away from the positive pole. This produces a potential difference of about 1.5 V.

30. Resistor Although every object resists current, a resistor has a measured value for resistance. There are resistors in every electronic device you own. http://www.jestineyong.com/?p=2340

31. Circuits are loops http://www.linkwitzlab.com/Pluto/woofer-asp.htm http://www.teachengineering.org/view_activity.php?url=http://www.teachengineering.org/collection/cub_/activities/cub_electricity/cub_electricity_lesson03_activity1.xml

32. The most important equation: Ohm’s Law: I = V / R What does it mean?...

33. What is Ohm’s law trying to tell us? I = V / R In simple objects, if you put twice as much potential difference across an object, then you will twice as much current in the object. [We call these objects “ohmic”.] If the object has twice as much resistance, then there will be half the current. This is a cause-effect pattern. Much like: a =  F / Mand  T = Q / Mc

34. Resistance depends on at least 3 things. Longer (‘L’ for length) objects have more resistance. More narrow objects have more resistance (‘A’ for area). Some materials resist flow more than others ( ‘  ’ for resistivity). See the table… R =  L/A

35. Resistivity for most materials is either very high (insulators) or very low (conductors). Material Resistivity  (Ohm meter) Glass1 x 10 12 Copper1 x 10 -8

36. Series vs. Parallel

37. Series Circuit http://www.petervaldivia.com/technology/electricity/types_of_currents.php

38. Three resistors in series R1R1 R3R3 R2R2

39. Parallel Circuit http://pzweb.harvard.edu/ucp/curriculum/circuits/s5_background.htm

40. Three resistors in parallel R1R1 R2R2 R3R3

41. What is the relationship between the currents? R1R1 R3R3 R2R2 I 3 I 1 I PS I 2 I 1 I 2 I 3 I PS PS

42. What is the relationship between the currents? R1R1 R3R3 R2R2 I 3 I 1 I PS I 2 I 1 = I 2 = I 3 = I PS This makes sense because the charge just goes around and around the single loop. PS

43. What is the relationship between the voltages? V 1 R1R1 R3R3 R2R2 V2V2 V3V3 V 1 V 2 V 3 V PS PS V PS

44. What is the relationship between the voltages? V 1 R1R1 R3R3 R2R2 V2V2 V3V3 V 1 + V 2 + V 3 = V PS This makes sense because the energy coming out of the resistors comes into the system from the power supply V PS PS

45. What is the relationship between the Resistances? R1R1 R3R3 R2R2 R 1 R 2 R 3 R EQ

46. What is the relationship between the Resistances? R1R1 R3R3 R2R2 R 1 + R 2 + R 3 = R EQ This makes sense because any one electron will need to go through all of the resistors.

47. What is the relationship between the currents? R1R1 R2R2 R3R3 I 1 I 2 I 3 I PS I 1 I 2 I 3 I PS

48. What is the relationship between the currents? R1R1 R2R2 R3R3 I 1 I 2 I 3 I PS I 1 + I 2 + I 3 = I PS This makes sense because the small streams make the big river.

49. What is the relationship between the voltages? V V V V R1R1 R2R2 R3R3 V 1 V 2 V 3 V PS

50. What is the relationship between the voltages? V V V V R1R1 R2R2 R3R3 V 1 = V 2 = V 3 = V PS This makes sense because each resistor is connected to the power supply.

51. What is the relationship between the resistances? R1R1 R2R2 R3R3 R 1 R 2 R 3 R EQ

52. What is the relationship between the resistances? R1R1 R2R2 R3R3 R EQ is less than the smallest resistance! This makes sense because each resistor is really a pathway !

53. What is the relationship between the resistances? R1R1 R2R2 R3R3 R EQ is less than the smallest resistance!

54. Batteries in series (What would be the effect?) http://pzweb.harvard.edu/ucp/curriculum/circuits/s5_background.htm

55. Measuring Current (Ammeters)

56. Ammeters go in the flow. R1R1 R3R3 R2R2 I 3 I 1 I PS I 2 PS

57. Measuring Voltage (Voltmeters)

58. Voltmeters go outside of the flow. V V V V R1R1 R2R2 R3R3

59. The Voltage Divider (1 of 4) If you needed 3 V to run a device, but you only had a 9 V battery, there is an important device that would come in handy: the Voltage Divider. You can build a voltage divider using two resistors…

60. The Voltage Divider (2 of 4) http://people.sinclair.edu/nickreeder/eet150/mod05.htm

61. The Voltage Divider (3 of 4) The total resistance is: 2000  + 1000  = 3000 . The current in the circuit is: I = V/R = 9V / 3000  = 0.003 A The voltage across the top resistor is V = IR = (0.003 A)(2000 W) = 6 V The voltage across the bottom resistor is V = IR = (0.003 A)(1000 W) = 3 V Hey, that’s exactly what we needed!

62. The Voltage Divider (4 of 4)

63. Sensors (part of what makes electricity so useful) Sensors are devices that take a non-electrical _ _ _ _ _ and produce an electrical _ _ _ _ _ _. This lets us measure temperature, acceleration, intensity of light and sound, force, and much more.

64. Sensors (part of what makes electricity so useful) Sensors are devices that take a non-electrical input and produce an electrical output. This lets us measure temperature, acceleration, intensity of light and sound, force, and much more.

65. Sensors ThermistorStrain (Force)

66. Sensors are often used as one of the resistors in a voltage divider. This allows the output voltage to be proportional to the quantity that we care about: temperature, weight, etc.

67. Internal Resistance (r) of a battery Charge moves through every element of a circuit (including batteries). Every object has atoms, so every object has resistance to current (including batteries). The resistance of a battery is handled with a special variable: r, the “Internal Resistance” of the battery.

68. Emf ( E ) We have a special name for the ideal potential difference made by an energy source: Electromagnetic Force ( E = Emf). This is the amount of chemical energy that has been changed to electrical energy (per charge). This applies to cells, batteries, generators, anything that changes energy of one sort into electrical energy.

69. Why is the voltage of a battery less than its emf? The potential difference (voltage) across a battery is less than the energy per charge that the chemicals made. Current in any object makes heat. V < E is due to the wasted energy of heating up the battery. The current moves through the cells and heats them. V = E – I r.

70. Power = V I The power that is delivered to the circuit is E I. The power that is taken out of the circuit is V I. If we use Ohm’s law we can see that power also can be written as I 2 R. If we use Ohm’s law again we can see that power also can be written as V 2 / R.