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Ch 20

Ch 20. ELECTRICITY. Static electricity. the accumulation of electric charges on an object opposite charges attract like charges repel. Charging by Friction. Dragging feet on carpet Rubbing balloon on hair Running comb through your hair

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Ch 20

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  1. Ch 20 ELECTRICITY

  2. Static electricity • the accumulation of electric charges on an object • opposite charges attract • like charges repel

  3. Charging by Friction • Dragging feet on carpet • Rubbing balloon on hair • Running comb through your hair • All have electrons transferred causing a negative charge

  4. Charging by Induction • charged objects cause electrons to rearrange their position on a neutral object, w/o contact • Ex: Electroscope

  5. detects the presence of electric charges • If a negatively charged item touches the knob, the leaves repel • If a positively charged item touches the knob, the leaves repel • An uncharged object has no effect on the leaves

  6. Electroscope

  7. Charging by Contact • Touching hand to Van De Graff generator

  8. Conductors and Insulators • Conductor-A material that allows electrons to move easily • Ex: metals, earth • Insulators-A material that does NOT allow electrons to move easily • Ex: plastic, wood, glass

  9. Electric Current • Flowing Electrons • a negatively charged object has more potential energy than uncharged objects • Two types: AC and DC • Electrons flow from places of higher potential energy to places of lower potential energy

  10. Circuit Symbols Conductor(wire) Switch Battery Bulb, light, lamp Motor Voltmeter Ammeter Resistor/resistance

  11. Circuit • a closed path through which electrons can flow

  12. Batteries • Dry Cell • Electrons flow from negative to positive • Wet Cell • Two metallic (different metals) plates in electrolyte solution

  13. Potential Difference • difference in potential between 2 different places • Measured in Volts (V) • Also called Voltage • Depends on a comparison of the energy carried by e- at different points • Measured with a voltmeter

  14. Current • the flow of electrons through a wire or any conductor • measured in Amperes (A) • Depends on the # of electrons passing a point in a given time • Measured with an Ammeter Voltmeter Ammeter resistor

  15. Resistance • The tendency for a material to resist the flow of electrons • Measured in Ohms () • Two things affect the amount of resistance in a conductor

  16. Resistance • Type of material • materials such as tungsten (filament in light bulbs) are very resistant to electron flow • higher resistance changes electrical energy into thermal energy and light

  17. Resistance • Size of conductor • Thin wires have higher resistance • Thick wires have low • Short wires have less resistance • Long wires have more

  18. Ohm’s Law • Potential difference = current x resistance • V = I x R • V=Voltage [V] • I=Current [A] • R=Resistance [] voltage current resistance

  19. Ohm’s Law • R=160 • I=15A • V=? • V=120V • R=3 • I=?

  20. Electrical Circuits:SERIES • Current has only one path it can travel along • No current flows if path is open • Current stays the same in series circuit for the circuit and across each resistor

  21. Electrical Circuits-PARALLEL • Contains separate branches for current to move through • More current flows through the paths of lowest resistance

  22. Electrical Circuits-PARALLEL • Potential difference (Voltage) stays the same in parallel circuits across each resistor and for the circuit • Current continues to flow through other branches if one branch is open

  23. Electrical Circuits

  24. Electrical Power • the rate at which electrical energy is converted to another form of energy • Measured in Watts (W) (or kW) • Power=current x voltage • P = I x V • [W] = [A] x [V]

  25. Electrical Power • An air conditioner used 1800W of power. The voltage source is 120V. How much current is flowing through the air conditioner?

  26. Electrical Power • A radio requires 0.25A of current when operated on a 120V source. How much power is used by the radio?

  27. Electrical Energy • The amount you use depends on the power required by appliances and how long they are used. • Energy=Power x time • E = P x t • [kWh] = [kW] x [h] • Unit is the kilowatt-hour

  28. Electrical Energy • The reading on an electric meter was 2345kWh for Jan and one month later it was 3456kWh. How much electrical energy was used for the month of Feb?

  29. Electrical Energy • How much would the electric bill for the month of Feb be if the electricity cost $0.10 per kilowatt-hour?

  30. IAN page 52:Series & Parallel Circuits • Define series and parallel circuits (from notes or book) • Draw each circuit from the notes. • Label each portion of the circuit from the notes

  31. Electrical Energy • A Blow Dryer is rated at 1,500 watts by the manufacturer. This is how much electric power it uses when it operates. If the Blow Dryer is operated for a total of 2 hours each month, the Blow Dryer consumes 1,500 watts x 2 hours = 3000 watt-hours. Since "Utility Rates" are based on kilowatt-hours, divide by 1,000 to get 3 kilowatt-hours. This shows how powerconsumption and operating time are important in determining energy use.

  32. IAN page 41: Ohm’s Law • At the top of the paper, write the equation for Ohm’s Law. • Define all variables & give units for each variable. • Glue/tape/staple problems under equation and solve all problems. • This can be done in pencil! • Highlight answer • Make sure to have units!

  33. Electrical Circuits-parallel • If looking for Resistance • Inverse, add, (equal) inverse 1 = 1 + 1 + 1 Req R1 R2 R3 … • If looking for currentof circuit • I=V/Req • If looking for the current in each resistor I1=V I2=V R1 R2…

  34. Electrical Circuits-parallel • A 9V battery is connected to four resistors: 2 , 4 , 5  , and 7  • Find the • Equivalent Resistance • Current in the circuit • Current in each resistor • voltage in each resistor

  35. Electrical Circuits-series • If looking for ResistanceReq=R1+R2+R3+… (eq = Equivalent Resistance) • If looking for voltage (p.d.)of circuit • V=IReq • If looking for voltageacross each resistor • V1=IR1 V2=IR2 V3=IR3 V4=IR4

  36. Electrical Circuits-series • A 9V battery is connected to four resistors: 2 , 4 , 5  , and 7  • Find the • Equivalent Resistance • Current in the circuit • voltage in each resistor • Current in each resistor

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