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Unit V :

Electricity. Unit V :. Essential Questions :  What is charge?  How do charges behave?.  What is an electric field?  How is electricity created?  What is resistance?  How do circuits work?. Electrostatics.

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Unit V :

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  1. Electricity Unit V: Essential Questions:  What is charge?  How do charges behave?  What is an electric field?  How is electricity created?  What is resistance?  How do circuits work?

  2. Electrostatics  The study of electric charges at rest along with their electric fields and potentials I. A. Electric Nature of Matter 1. Sketch: 2. Concept Map: the Atom

  3. Charge is Charge is Symbol Symbol Symbol Mass of Inside Nucleus Outside Nucleus Charge is Mass of Mass of

  4. B. The Elementary Charge: the magnitude of charge on a proton or an electron 1. Symbol: e 2. Protons and Electrons have equal but opposite charges • Protons are 1 positive elementary charge: • Electrons are 1 negative elementary charge:

  5. 3. Any object may only have a charge that is a multiple of e i.e.: 4. Charge is said to be quantized  comes in discreet bundles or packages

  6. C. Charged Objects 1. Objects with excess electrons or a deficit of electrons  As the amount of electrons increases, the charge of an object becomes more ___________ 2. Atoms that have gained or lost electrons are called ___________  Electrons are removed when an atom gains energy NEGATIVE IONS (Friction, Heat, Light)

  7. REPEL ATTRACT 3. Like charges ___________ while opposite charges ____________  The charges exert __________ on each other 4. Charge is Conserved!  Neither created nor destroyed, only transferred Force Law of Conservation of Charge

  8. 5. Charge will spread itself out evenly over objects in contact!

  9. 6. Grounding: All charges seek the path of least resistance to the ground (where they can “get away from each other”)  most objects that are connected to the ground will allow charge to pass through Including YOU!

  10. 7. Charge has Units!  Coulombs (C)  1 Coulomb = 6.25 x 1018 elementary charges  1 elementary charge = 1.6 x 10-19C  How can you remember these numbers? PRT’s !! (Front Cover)

  11. Example: Charges • If an object contains 3.45 x 1013 elementary charges, how many Coulombs of charge are on the object? • How many MICROCoulombs is the equal to? • How many elementary charges make up an –8.0 Coulomb charge? • What is causing the charge for this object?

  12. Journal # 11/18 A sphere has an excess of 1.5625 x 1017 elementary charges. • How many Coulombs of charge exist on the sphere? • How many Microcoulombs of charge does the sphere posses? • Calculate the electrostatic force that would exist if the sphere were brought within 0.5 meter of an identical NEGATIVELY charged sphere.

  13. 8. Charge is Transferable a. Conductors: objects that allow charge to move freely through b. Insulators: objects that slow or prevent the flow of charge Examples: metal, tap water, YOU Examples: most plastic, rubber, distilled water

  14. c. Conduction: transfer of charge by contact between objects  electrons move between objects

  15. d. Induction: transfer of charge between two objects without contact  electrons move to/from the ground

  16. quantifies electrostatic force between charges D.Coulomb’s Law: 1. As the magnitude of the charges increases the force between them _______________ increases 2. As the distance between the charges increases the force between them __________________ decreases (by a lot)

  17. 3. Equation: Electrostatic Force (N) Electrostatic Constant or Coulomb’s Constant ( ) N • m2/C2 Magnitude of Charge (C) Separation of Charges (m) NOT RADIUS!

  18. 4. Units: 5. Electrostatic Force is a vector quantity has magnitude and direction

  19. Example: Coulomb’s Law • What is the electrostatic force between a charged boy and girl at the Homecoming possessing net charges of +2.0 microcoulombsand –3.0 microcoulombs if the lovers are 10 meters apart? • Is the force attractive or repulsive?

  20. Example: Converting Charge How many Coulombs are in 850 microcoulombs? How many microcoulombs are in 2.8 x 10-6 C? How many microcoulombs are in 0.003 C? How many meters are in 80 cm?

  21. Region around a charged object in which force is exerted on another charged object E. Electric Fields 1. Electric fields are shown with electric field lines a. lines are drawn along the path a “positive test charge” would move in the field b. all lines are directed toward the negative charge Fields

  22. 2. Examples of electric fields a. Positive Point Charge b. Negative Point Charge c. Positive and Negative Spheres

  23. d. Positive Sphere vs. Positive Sphere e. Negative Sphere vs. Negative Sphere

  24. f. Oppositely Charged Parallel Plates

  25. The work done by moving a charge in an electric field F. Potential Difference 1. When work is done on a charge, there is a change in its electric potential energy

  26. 2. Potential Difference (V) is equal to the work done (W) per unit charge (q) 3. Equation: 4. Units: PRT’s !! (Electricity Section)

  27. Example 1: Potential Difference Moving a charge of 3.2 x 10-19 C between two points in an electric field requires 4.8 x 10-18 J of energy. What is the potential difference between these points?

  28. 6. In order to bring like charges closer together, Work must be done! Same is true for separating unlike charges! 7. Potential Difference can also be used to find the work done in moving a charge 

  29. No Work Done Here! Work IS Done Here!

  30. Example 2: Potential Difference How much charge is in a wire containing 1.5625 x 1018 elementary charges? How much work is done to move these charges through a potential difference of 120V?

  31. 9. Potential Difference is measured with a Voltmeter

  32. Example: Electric Fields Identify the sign of the charges that exist on the spheres in the following situation:

  33. II. Provides a pathway for charges to flow Electric Circuits A. Electric Current: 1. Conditions necessary for electric current:  a potential difference (V) must exist  a closed circuit (pathway) must exist  the pathway must be a conductor The rate at which charge is allowed to flow past a given point (over time)

  34. I = Electric Current Δq = total charge t = time 2. Equation: 3. Units:

  35. 4. Direction of Current Flow a. Only electrons are allowed to move freely – toward positive charge! b. Current is usually understood as flowing from positive to negative  Conventional Current

  36. increase 5. In general, As the potential difference increases, the electric current will___________ 6. Electric Current is measured with an Ammeter Direct Relationship Current (A) Potential Difference (V)

  37. 7. Direct vs. Alternating Current a. Direct Current: electrons flow in one direction only  produced by batteries, cells, and automobiles  weakens considerably when resistance is present  length of wire  temperature

  38.  used to deliver electricity to end users b. Alternating Current: switches direction of electron flow with a determined frequency  requires high potential differences to drive the current  allows current to maintain strength over large distances

  39. B. Circuit Symbols and Diagrams  makes it possible to represent circuits easily  wire is shown as lines  the rest of the symbols we use are in the PRT’s! PRT’s: Electricity Section Measures potential difference  Measures current Slows down current  Adjustable (Rheostat)  Acts as a resistor

  40. Journal #23 11/21 A 12 Volt battery is used to power a circuit with a switch and three light bulbs. 100 Coulombs of charge move through the circuit in 20 seconds. How much work is done to move this charge? What is the electric current? Draw a circuit diagram!

  41. Ammeters must be placed in SERIES so that all current passes through in order to measure current! Voltmeters must be placed in PARALLEL (across) a circuit item to measure the Voltage

  42. Example: Circuit Diagram Draw a circuit with three light bulbs (one after the other) that also contains a switch, a battery, and a properly placed ammeter and voltmeter.

  43. Opposition a conductor or device offers to electric current C. Resistance: 1. A potential difference is created by resistance and current is slowed down

  44. I = Electric Current V = Potential Diff. R = Resistance 2. Equation:  3. Units: Ohm’s Law

  45. Journal #24 11/22 A 120 Volt outlet is used to power a circuit with some resistance. If 60 Coulombs of charge move through the circuit in 10 seconds, what is the electric current? How much work is done by the outlet moving the charge? What is the internal resistance of the circuit? How long will it take for 400 Coulombs of charge to flow through the circuit?

  46.  Longer wire = more resistance 4. Factors Affecting Resistance a. Length of Wire b. Thickness of Wire  Related to diameter of wire!  Thicker wire = less resistance

  47. How well a material conducts electrons c. Resistivity:  Depends on material PRT’s: Electricity Section

  48. d. Temperature of conductor (wire)  Warmer temperatures increase collisions of electrons with otherparticles/atoms and slows down current!  Warmer temperatures increase resistance

  49. All Components are connected in sequence (one after another) D. Series Circuits: 1. Each resistor will cause a “potential drop”  sum of potential drops will be the total voltage across the series circuit 

  50. 2. Each individual resistance can be added together to find the total equivalent resistance for the series circuit (AKA effective resistance) 

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