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Bellringer

Bellringer. What are some ways that you use electricity in your daily life?. Objectives. We will investigate electricity as you are used to seeing it, and using it at home Learn what electric current is and what an electric circuit it. Electrostatics Test.

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Bellringer

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  1. Bellringer What are some ways that you use electricity in your daily life?

  2. Objectives We will investigate electricity as you are used to seeing it, and using it at home Learn what electric current is and what an electric circuit it

  3. Electrostatics Test I will have your grades by the end of the day. Does 100=99.999999999999forever?

  4. Does 100=99.999999999999999? Yes!

  5. Electric Current and Circuits

  6. Electricity as you know it! • Electric Current is a flow of charged particles. • Conventional Current is the direction in which a positive test charge moves. • The flow of electrons and conventional current are in opposite directions

  7. Electric Current Electric Current is measured in Amperes (A, or amps) 1 Ampere is equal to 1Coulomb moved past a single point in 1 second

  8. Electric Current Electric current is the measure of electrons moving past a certain point. Much like the current of a river is measure by the amount of water moving past a certain point.

  9. Electric Current I is current measured in Amperes (A) Delta q is charge measured in Coulombs(C) t is time measured in seconds (s)

  10. Amps 0.001-0.01 Amps = Little to no shock 0.01-0.02 Amps = Painful shock 0.02-0.075 Amps= Serious shock, muscle control lost 0.075-0.1 Amps = Heart misses beats 0.1-0.2 Amps= Changes heart’s rhythm, possible death

  11. Amps Over 0.2 Amps = Severe burns and muscle contraction. Heart stops from chest muscle pressure. Internal organs are damaged. Can survive if you are removed from the circuit fast enough. Very painful recovery, but heart very likely to go back to its regular beat

  12. Amps If a wire has 1 amp of current running through it should you touch it? http://www.youtube.com/watch?v=umDr0mPuyQc

  13. Examples If 2.5 Coulombs move past a point in 3 seconds, what is the current?

  14. Practice What is the current of a 6C charge that moves past a point in 2.5 seconds? I=2.4 Amperes How long does it take a 5 amp current to move 3 Coulombs of charge past a single point? t=0.6 seconds

  15. Potential Difference

  16. Potential Difference CHARGE PUMP

  17. Electric Circuits • Electric Circuit: Any closed loop or conducting path allowing electric charges to flow. • All circuits must have two things: • Charge pump (to increase electric potential) • Something to reduce the electric potential

  18. Moving Electrons • Light Bulb Demo • Difference between plugged in and out

  19. Checkpoint What is electric current? What is an electric circuit?

  20. Transformation of Energy Motor Positive Charges Positive Charges Gen.

  21. Infinite Energy Idea Could a machine like this produce an infinite cycle of energy? Why? Where is the energy lost?

  22. Bellringer DO WORK STOP What is the current in a wire if 0.25C of charge passes a point in 0.5 s?

  23. Objectives Recreate Ohm’s discover of Ohm’s Law, and practice its application. Learn how to draw schematic diagrams of electrical circuits. Learn about “electrical friction” in long wires and other objects

  24. Energy Lost in Wires Just like friction in mechanics, electric circuits have friction that cause energy to be lost. It is called “Resistance”

  25. Ohm’s Law Around 1825 Ohm was experimenting with electricity when he noticed an important trend between the current in a circuit and the voltage.

  26. Investigating Ohm’s Law For the sake of science will recreate Ohm’s experiment to see if we can come up with Ohm’s Law on our own!

  27. Discovering Ohm’s Law • Record this data! • Supplies: • Voltmeter • Ammeter • Wires • Batteries

  28. Ohm’s Law R is the resistance measured in Ohms (Ω) V is the potential difference measured in Volts (V) I is the current measured in Amperes (A)

  29. Resistance The resistance of an object in a circuit can be thought of like a frictional force because it makes it harder for the electrons to move.

  30. Resistance Demos How can we tell that electrical energy is being “lost” due the resistance of these objects? Hotdog Demo Pickle Demo

  31. Example What is the resistance of a light bulb that has a current of 2A running through it and is connected to a 120 volt power source? R=60Ω

  32. Practice What is the current running through a 100 Ohm motor that is connected to a 120 V source? 1.2A What is the voltage across a hotdog that has a resistance of 10 Ohms and has 0.2 amps running through it? 2V

  33. Schematics http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

  34. Schematics The easiest way to describe the different parts of a circuit is with a Schematic A schematic is a diagram that symbolically represents and simplifies a circuit

  35. Schematics Different symbols are used for different parts of a circuit The symbols you need to know are found on your reference table

  36. Schematic Symbols

  37. Schematics The positive side of the battery is the longer end. To show the current through the circuit you draw arrows showing which ways positive charges would flow.

  38. Schematic Practice If the diagram to the right has a 1.5V battery hooked up to it, why won’t the light turn on?

  39. Schematic Practice What is the current in the circuit? I = 2 amps

  40. Schematic Practice Name all the elements in this circuit. 3 cell battery Ammeter Resistor Voltmeter Wires

  41. Bellringer DO WORK STOP What is the resistance in a wire that is connecting both ends of a 9 volt battery and has a current of 1.5 A running through it?

  42. Objectives Review your schematics from last night Learn about how different materials have different resistances. Variable Resistance Demos

  43. Picture Practice On page 603 answer questions 8 through 11

  44. Physics Trip Darien Lake May 19th? Is Darien Lake nice? Is it worth e-mailing them for more information?

  45. Resistance in the Wires In schematics we will ignore the resistance in the wires. (Much like we ignore air resistance). But this will not always be the case.

  46. Resistance in a Wire In real life it is often important to know how much voltage you lose due to resistance in a wire. It is easy to calculate!

  47. Resistance in a Wire R is the resistance in the wire measured in Ohms (Ω) is the resistivity of the wire measured in Ohms*meter (Ω*m) L is the length of the wire measured in meters (m) A is the cross-sectional area of the wire measured in meters squared ()

  48. Resistivity Resistivity is a property of each material. It is a constant number that is different for each material.

  49. Example What is the resistance in a copper wire that is 2km long, and has a cross sectional area of ()?

  50. Practice What is the resistance is a nichrome wire that is 12 meters long and has a cross sectional area of ? 3.6 ohms What is the resistance of a gold wire that has a length of 1 meter and a diameter of 1mm? 0.031ohms

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