1. Electric Charges & Current Chapter 20

2. Types of electric charge Protons w/ ‘+’ charge “stuck” in the nucleus Protons w/ ‘+’ charge “stuck” in the nucleus Electrons w/ ‘-’ charge freely moving around the nucleus in orbits Electrons w/ ‘-’ charge freely moving around the nucleus in orbits

3. Conductors Allow the easy flow of electricity Allow the easy flow of electricity loosely bound electrons that are free to move from atom to atom loosely bound electrons that are free to move from atom to atom metals like aluminum, gold, copper and silver metals like aluminum, gold, copper and silver

4. Insulators Insulators – resists the flow of electrons Insulators – resists the flow of electrons hold more tightly to their valence electrons: hold more tightly to their valence electrons: plastic, rubber, glass plastic, rubber, glass

5. Interactions between charges same as in magnetism same as in magnetism Unlike magnetism were on a magnet there is always a + on one end and a – on the other end of the magnet Unlike magnetism were on a magnet there is always a + on one end and a – on the other end of the magnet electrical charges can exist alone electrical charges can exist alone Like charge repel Like charge repel Opposite charges attract Opposite charges attract

6. Electric Fields Exert a force through the force field in all directions from the charged particle Exert a force through the force field in all directions from the charged particle When a charged particle enters the force field of another particle it is either attracted or repelled When a charged particle enters the force field of another particle it is either attracted or repelled The diagram represents stronger force as the lines get closer & closer together The diagram represents stronger force as the lines get closer & closer together

7. Static Charge Latin word “Stasis” which means “Stays” Latin word “Stasis” which means “Stays” Objects are typically “Neutral” w/ the same # of protons and electrons Objects are typically “Neutral” w/ the same # of protons and electrons They can become “charged” by gaining or losing electrons – They can become “charged” by gaining or losing electrons – NOT PROTONS! – They stay in the nucleus! NOT PROTONS! – They stay in the nucleus! The buildup of these charges is “Static Electricity” The buildup of these charges is “Static Electricity” In Static Electricity the charges build up and STAY; In Static Electricity the charges build up and STAY; they don’t flow as they do in electric currents they don’t flow as they do in electric currents

8. Transferring Static Charge Friction – transferred from rubbing i.e. get shocked after walking on the carpet Friction – transferred from rubbing i.e. get shocked after walking on the carpet Conduction – transferred by direct contact w/ another object – hair standing on end w/ Van de Graff machine Conduction – transferred by direct contact w/ another object – hair standing on end w/ Van de Graff machine Induction – the force field of a highly negatively charged object pushes the electrons away from nearby objects causing them to become + charged, they then are attracted to each other. i.e. statically charged balloon attracts small pieces of torn up paper Induction – the force field of a highly negatively charged object pushes the electrons away from nearby objects causing them to become + charged, they then are attracted to each other. i.e. statically charged balloon attracts small pieces of torn up paper

9. Static Discharge Objects don’t hold a static charge forever – objects tend toward equilibrium – they “want” to be neutral Objects don’t hold a static charge forever – objects tend toward equilibrium – they “want” to be neutral When electrons move toward this equilibrium – static discharge occurs When electrons move toward this equilibrium – static discharge occurs Humidity – water (a polar molecule) vapor in the air pulls electrons off negatively charged objects, preventing static charges to build up Humidity – water (a polar molecule) vapor in the air pulls electrons off negatively charged objects, preventing static charges to build up Sparks & Lightning - objects reaching static equilibrium Sparks & Lightning - objects reaching static equilibrium

10. Homework Read pages: 682-689 Complete Guided Reading Handout on Electric Charge and Static Electricity Due Weds 6/4

11. Chp. 20 Electric Current & Circuits Objectives: Define Voltage Define Electric Current Describe conditions that allow current flow Explain how resistance affects current flow

12. Circuit Measurements Electric Current - Flow of electrons through a material Electric Current - Flow of electrons through a material Electrical Potential – Electrical Potential – Similar to potential energy (lifting something higher against the force of gravity gives it greater potential to do work, increasing its potential energy.) Similar to potential energy (lifting something higher against the force of gravity gives it greater potential to do work, increasing its potential energy.) When given the opportunity, objects will move from higher potential energy to an area of lower potential energy When given the opportunity, objects will move from higher potential energy to an area of lower potential energy Electrical potential is related to their electrical fields and not to height – as electrons build up on one side they “want” to flow to an area w/ less potential Electrical potential is related to their electrical fields and not to height – as electrons build up on one side they “want” to flow to an area w/ less potential

13. Voltage (Potential Difference)

14. Potential Difference (Voltage) Potential Difference is the work required to move +1C of charge from one terminal through the device to the other terminals (Not through something attached to the device) Unit is the volt, V 1 volt = 1 Joule/Coulomb (Joule is unit for Energy & Work) Potential Difference is often called Voltage

15. Voltage Voltage – causes current to flow through an electrical circuit Voltage – causes current to flow through an electrical circuit Volt – unit of measure to measure this potential Volt – unit of measure to measure this potential A Voltage Source (battery or generator) is required to maintain the electrical potential in a circuit. A Voltage Source (battery or generator) is required to maintain the electrical potential in a circuit.

16. Potential Difference Simple Battery Example showing electrons flowing in a simple circuit http://phet.colorado.edu/en/simulation/batter y-resistor-circuit http://phet.colorado.edu/en/simulation/batter y-resistor-circuit

17. CURRENT Electricity is basically the movement of electrons

18. Current Current – rate at which charges move in a conductor  Charges move to a position of lower potential energy  When this happens an electric current is produced  Current is abbreviated with an “ I ” Unit of current is the “Ampere” or Amps, A 1 A = 1 Coulomb of Electrons / Second

19. Electrical Current Water flowing thru a pipe depends on more than the angle of the pipe. It also depends on the length of the pipe, diameter of the pipe and if the pipe is clogged or open. Water flowing thru a pipe depends on more than the angle of the pipe. It also depends on the length of the pipe, diameter of the pipe and if the pipe is clogged or open. Electrical Current is measured in Amperes Electrical Current is measured in Amperes Amount of Electrical Current ( amps) depends on more than just Voltage, it depends on the Resistance found in the circuit. Amount of Electrical Current ( amps) depends on more than just Voltage, it depends on the Resistance found in the circuit.

21. Current How do lights come on instantly when I flick the switch? You don’t have to wait for 1 electron to make a complete circuit. There are electrons “waiting” all along the wire. Each electron pushes the one ahead of it, so as soon as the first electron starts to move, the last electron in the wire moves into the light bulb.

22. RESISTANCE Resistance works AGAINST current

23. Resistance – Ohms Resistance, R:  Caused by internal friction  Slows the movement of charges through a conducting material  Unit of measure is the ohm (Ω) Recall… Friction results in Heat

24. Water Hose Example Electricity in a Wire is a lot like Water in a Hose Voltage is how much pressure is applied to push the water through the hose Current is how fast the water flows through the hose Resistance is the friction in the hose

25. Resistance Amount of Resistance can Vary: In our water hose example, changing the following will change the amount of Resistance –Diameter of hose –Length of hose –Material (changes the amount of friction) The Same would be true for a WIRE http://phet.colorado.edu/sims/resistance-in- a-wire/resistance-in-a-wire_en.htmlhttp://phet.colorado.edu/sims/resistance-in- a-wire/resistance-in-a-wire_en.html

26. What Influences Resistance in a wire? Material of wire – aluminum and copper have low resistance Thickness – the thicker the wire the lower the resistance Length – shorter wire has lower resistance Temperature – lower temperature has lower resistance

27. Resistance Resistance is a good thing because it reduces the actual volts something gets Just like a dam Resistor: –Special type of conductor used to control current

28. Resistance Resistance can be a bad thing… Energy can be lost as electricity travels a long distance…

29. Electric Current Homework: Read pages 692 to 699 Do Review & Reinforce/Guided Reading Handout Due Monday 6/9

30. Chp. 20 Resistance and Ohms Law Objectives: Define Resistance Describe Ohms Law Calculate current, voltage or resistance in a circuit using ohms law

31. Current, Voltage & Resistance Pressure in the hose (V), rate the water flows through the hose (I) and the type of hose (R) are all related.  If you change one, it affects the others The relationship is known as Ohm’s Law… Voltage = Current x Resistance V = I x R

32. Ohms Law

33. Learning Target: Use Ohm's Law to calculate current, voltage, and resistance using correct units.

34. Ohm’s Law

35. Practice: There is a potential difference of 12 volts across a resistor with 0.50 amps of current in it. The resistance of the resistor is _________. A. 0.5 ohms B. 6 ohms C. 12 ohms D. 24 ohms

36. Practice: If there is a current of 6 amps flowing through a 3 ohm resistor, what is the potential difference in the circuit? A. 0.5 volts B. 2 volts C. 9 volts D. 18 volts

37. Practice: If a circuit has a potential difference of 120 volts and a resistance of 10 ohms, what is the current that flows through the circuit? A. 0.08 amps B. 12 amps C. 120 amps D. 1200 amps

38. Ohms Law Homework: Read pages 451 – 454 Do Review & Reinforce handout and practice problems 5-9 Due Monday 6/9

39. Series Circuits Series Circuits – provides only one path for the electrons to follow Series Circuits – provides only one path for the electrons to follow 1. A break in the circuit stops the flow of electricity to all other parts of the circuit 1. A break in the circuit stops the flow of electricity to all other parts of the circuit 2. With multiple light bulbs (more resistance) the current reduces & the dimmer the lights become 2. With multiple light bulbs (more resistance) the current reduces & the dimmer the lights become 3. Ammeters should be wired in series 3. Ammeters should be wired in series

40. Parallel Circuits Parallel circuits – the different parts of the circuit are on separate branches Parallel circuits – the different parts of the circuit are on separate branches A break (burn out light bulb) in the circuit doesn’t stop the flow to the remaining devices A break (burn out light bulb) in the circuit doesn’t stop the flow to the remaining devices Multiple light bulbs will remain the same brightness since the resistance is not decreasing as it does in a series circuit. Multiple light bulbs will remain the same brightness since the resistance is not decreasing as it does in a series circuit. Each pathway can be separately switched off w/out affecting the others Each pathway can be separately switched off w/out affecting the others Household circuits – Wired in parallel, with a standard of 120 volts Household circuits – Wired in parallel, with a standard of 120 volts Voltmeters are wired in parallel Voltmeters are wired in parallel

41. Parallel Circuits The more paths the LESS the resistance The more paths the LESS the resistance Water example again: added pipes coming from a large tank will allow more water to flow out that a single pipe. Water example again: added pipes coming from a large tank will allow more water to flow out that a single pipe. Therefore as resistance degreases, current increases; they are inversely proportional Therefore as resistance degreases, current increases; they are inversely proportional

42. Schematic Diagrams All circuits need at least the following All circuits need at least the following Power supply, wire, resistors, other items include switches, connectors, meters, etc. Power supply, wire, resistors, other items include switches, connectors, meters, etc. There is a set of standard symbols used to represent these items in a diagram of the circuit There is a set of standard symbols used to represent these items in a diagram of the circuit

43. That’s all for Chapter 20

44. Power –Watts (W) Recall from last term… Power – rate that work is done at Units are Watts The higher the Watts, the higher the energy output per unit of time.

45. Power - Electricity Power = work/unit time P = v x I = Unit of measure is the Watt (W) 1 W = 1 J/sec

46. How is Electrical Power calculated? Electrical Power is the product of the current (I) and the voltage (v) The unit for electrical power is the same as that for mechanical power in the previous module – the watt (W) Example Problem: How much power is used in a circuit which is 110 volts and has a current of 1.36 amps? P = I V Power = (1.36 amps) (110 V) = 150 W