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Electrical Energy and Currents
Chapter 17
Pg. 592-625
+




17.1 Electric Potential
Pg. 594-601
+
            What do you think?
•   You may have purchased batteries for
    radios, watches, CD players, and other elect...
+
    Electric Potential Energy


     Potentialenergy associated with a charge
     due to its position in an electric f...
+
    Electrical Potential Energy

     A uniform
              electric field exerts a force on a
     charged particle ...
+
    Electrical Potential Energy

        PEelectric is positive if the charge is negative and
        moves with the fi...
+
    Classroom Practice Problem


     A uniformelectric field strength of 1.0 x 106
     N/C exists between a cloud at ...
+
    Classrom Practice Problem


     PEelectric   = -qEd
     PEe=   (-25)(1.0 X 106)(1500)
     Answer:      -3.75 x...
+
    Potential Difference

     Potential difference( V) is the change in
     electrical potential energy per coulomb o...
+
    Potential Difference


     Thepotential difference is calculated
     between two points, A and B.
      The   fi...
+
    Batteries

     A battery
              maintains a constant potential difference
     between the terminals.
     ...
+
            Now what do you think?
     You may have purchased batteries for
     radios, watches, CD players, and othe...
+




17.2 Capacitance
Pg 602- 607
+
                What do you think?
    •    If a light bulb replaced the two metal plates and the
         battery was c...
+
    Capacitors
 A device        that is used to store PEelectric
 The    two metal plates are electrically neutral
   ...
+
    Parallel Plate Capacitors

     Electrons build up on the left plate, giving it a
     net negative charge. The rig...
+
    Capacitance

 Capacitance     measures the ability to store charge.
 SI   unit: coulombs/volt (C/V) or farads (F)
...
+
    Capacitance


     How would capacitance change if the metal
     plates had more surface area?
      Capacitance ...
+
    Dielectrics
 The    space between the plates is filled with a
    dielectric.
     Rubber,   waxed paper, air

 T...
+ Capacitor Applications



  Connecting the two plates of a charged
  capacitor will discharge it.
   Flash
        att...
+
    Energy and Capacitors
     Asthe charge builds, it requires more and more
     work to add electrons to the plate d...
+
    ???? Classroom Practice Problem


     A 225  F is capacitor connected to a 6.00
     V battery and charged. How mu...
+
             Now what do you think?


     Ifa light bulb replaced the two metal
      plates and the battery was conne...
+




17.3 Current and Resistance
Pg 608-617
+
            What do you think?

    •   The term resistance is often used when
        describing components of electric...
+
    Electric Current


     Electric
             current (I) is rate at which charges flow
     through an area.
    ...
+
    Conventional Current

 Conventional     current (I) is defined as the
    flow of positive charge.
     The flow o...
+
    Resistance to Current

     Resistance     is opposition to the flow of charge.
      SI   unit: volts/ampere (V/A...
+
    Classroom Practice Problems

     A typical100 W light bulb has a current of
     0.83 A. How much charge flows thr...
+
    Classroom Practice Problems


     I=   Q/t        or   Q= It
     Q=    (0.83)(3600)
      2988       C
     We...
+
    Classroom Practice Problems

     This same 100 watt bulb (from the previous
     question) is connected across a 1...
+
    Resistance of a Wire


     On the next slide, predict the change
     necessary to increase the resistance of a
  ...
+
+
    Applications

     Resistors   in a circuit can change the current.
      Variableresistors (potentiometers) are u...
+
               Now what do you think?
    •   The term resistance is often used when
        describing components of el...
+




17.4 Electric Power
Pg. 618-623
+
                What do you think?
    •   Hair dryers, microwaves, stereos, and other
        appliances use electric p...
+
    Types of Current - Direct

     Batteriesuse chemical energy to give electrons
     potential energy.
        Ther...
+
    Types of Current - Alternating

                    Generators   change
                     mechanical energy into...
+
    Energy Transfer

                       Is
                         the electrical potential energy
               ...
+
    Energy Transfer
     A to B (unchanged)
     B to C (lost in bulb)
     C to D (unchanged)
     D to A (gained i...
+
    Electric Power

      Click below to watch the Visual Concept.



                         Visual Concept
+
    Electric Power
 Power     is the rate of energy consumption ( PE/ t ). For
    electric power, this is equivalent t...
+
    Classroom Practice Problems

     A toasteris connected across a 120 V kitchen
     outlet. The power rating of the...
+
    Classroom Practice Problems


     What   is the resistance of the toaster?
     V=   120v        I= 7.7A         ...
+
    Classroom Practice Problems


     How    much energy is consumed in 75.0 s?
     Energy   =P t
     P=   925 W  ...
+
    Household Energy Consumption

     Power      companies charge for energy, not
     power.
      Energy   consumpt...
+
    Electrical Energy Transfer

     Transfer
             of energy from power plants to your
     neighborhood must b...
+
          Now what do you think?
 Hair   dryers, microwaves, stereos, and other
    appliances use electric power when ...
+
    NOT NEEDED??? Gravitational
    Potential Difference
       Suppose a mass of 2.00 kg is moved from point A straigh...
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Electrical Energy and Currents Slide 1 Electrical Energy and Currents Slide 2 Electrical Energy and Currents Slide 3 Electrical Energy and Currents Slide 4 Electrical Energy and Currents Slide 5 Electrical Energy and Currents Slide 6 Electrical Energy and Currents Slide 7 Electrical Energy and Currents Slide 8 Electrical Energy and Currents Slide 9 Electrical Energy and Currents Slide 10 Electrical Energy and Currents Slide 11 Electrical Energy and Currents Slide 12 Electrical Energy and Currents Slide 13 Electrical Energy and Currents Slide 14 Electrical Energy and Currents Slide 15 Electrical Energy and Currents Slide 16 Electrical Energy and Currents Slide 17 Electrical Energy and Currents Slide 18 Electrical Energy and Currents Slide 19 Electrical Energy and Currents Slide 20 Electrical Energy and Currents Slide 21 Electrical Energy and Currents Slide 22 Electrical Energy and Currents Slide 23 Electrical Energy and Currents Slide 24 Electrical Energy and Currents Slide 25 Electrical Energy and Currents Slide 26 Electrical Energy and Currents Slide 27 Electrical Energy and Currents Slide 28 Electrical Energy and Currents Slide 29 Electrical Energy and Currents Slide 30 Electrical Energy and Currents Slide 31 Electrical Energy and Currents Slide 32 Electrical Energy and Currents Slide 33 Electrical Energy and Currents Slide 34 Electrical Energy and Currents Slide 35 Electrical Energy and Currents Slide 36 Electrical Energy and Currents Slide 37 Electrical Energy and Currents Slide 38 Electrical Energy and Currents Slide 39 Electrical Energy and Currents Slide 40 Electrical Energy and Currents Slide 41 Electrical Energy and Currents Slide 42 Electrical Energy and Currents Slide 43 Electrical Energy and Currents Slide 44 Electrical Energy and Currents Slide 45 Electrical Energy and Currents Slide 46 Electrical Energy and Currents Slide 47 Electrical Energy and Currents Slide 48 Electrical Energy and Currents Slide 49 Electrical Energy and Currents Slide 50
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Electrical Energy and Currents

  1. 1. + Electrical Energy and Currents Chapter 17 Pg. 592-625
  2. 2. + 17.1 Electric Potential Pg. 594-601
  3. 3. + What do you think? • You may have purchased batteries for radios, watches, CD players, and other electronic devices. Batteries come in a variety of different sizes and voltages. You probably have 1.5 volt, 3 volt, and 12 volt batteries in your home. • What do volts measure? • Is the number of volts related to the size of the battery? • How is a 3 volt battery different from a 1.5 volt battery?
  4. 4. + Electric Potential Energy  Potentialenergy associated with a charge due to its position in an electric field  Electrical potential energy is a component of mechanical energy  M. E. is conserved so long as friction and radiation are not present  Electrical potential energy can be associated with a charge in a uniform field
  5. 5. + Electrical Potential Energy  A uniform electric field exerts a force on a charged particle moving it from A to B.  Will the particle shown gain or lose PEelectricas it moves to the right?  Lose energy (because it is moving with the force, not against it)  Similar to a falling object losing PEg  PEelectric = Wdone = Fd = -qED
  6. 6. + Electrical Potential Energy  PEelectric is positive if the charge is negative and moves with the field.  PEelectric is positive if the charge is positive and moves against the field.
  7. 7. + Classroom Practice Problem  A uniformelectric field strength of 1.0 x 106 N/C exists between a cloud at a height of 1.5 km and the ground. A lightning bolt transfers 25 C of charge to the ground. What is the change in PEelectric for this lightning bolt?  d= 1,500m q= 25C  E= 1.0 X 106 N/C PEelectric= ??
  8. 8. + Classrom Practice Problem  PEelectric = -qEd  PEe= (-25)(1.0 X 106)(1500)  Answer: -3.75 x 1010 J of energy
  9. 9. + Potential Difference  Potential difference( V) is the change in electrical potential energy per coulomb of charge between two points.  Depends on the electric field and on the initial and final positions  Does not depend on the amount of charge  SI unit: joules/coulomb (J/C) or Volts (V)
  10. 10. + Potential Difference  Thepotential difference is calculated between two points, A and B.  The field must be uniform.
  11. 11. + Batteries  A battery maintains a constant potential difference between the terminals.  1.5 V (AAA, AA, C and D cell) or 9.0 V or 12 V (car)  In1.5 V batteries, the electrons use chemical energy to move from the positive to the negative terminal.  They gain 1.5 joules of energy per coulomb of charge  When connected to a flashlight, the electrons move through the bulb and lose 1.5 joules of energy per coulomb of charge.  Sort of like a concentration gradient.
  12. 12. + Now what do you think?  You may have purchased batteries for radios, watches, CD players, and other electronic devices. Batteries come in a variety of different sizes and voltages. You probably have 1.5 volt, 3 volt, and 12 volt batteries in your home.  What do volts measure?  Is the number of volts related to the size of the battery?  How is a 3 volt battery different from a 1.5 volt battery?
  13. 13. + 17.2 Capacitance Pg 602- 607
  14. 14. + What do you think? • If a light bulb replaced the two metal plates and the battery was connected, electrons would flow out of the negative and into the positive terminal. Will this also occur with the two metal plates? • If not, why not? • If so, is the flow similar or different from that with the light bulb? Explain. • The battery shown has a potential difference of 6.0 volts. It has just been connected to two metal plates separated by an air gap. There is no electrical connection between the two plates and air is a very poor conductor.
  15. 15. + Capacitors  A device that is used to store PEelectric  The two metal plates are electrically neutral before the switch is closed. What will happen when the switch is closed if the left plate is connected to the negative terminal of the battery?  Electrons will flow toward lower PE.  From the battery to the left plate  From the right plate to the battery
  16. 16. + Parallel Plate Capacitors  Electrons build up on the left plate, giving it a net negative charge. The right plate has a net positive charge.  Capacitors can store charge or electrical PE.
  17. 17. + Capacitance  Capacitance measures the ability to store charge.  SI unit: coulombs/volt (C/V) or farads (F)  In what way(s) is a capacitor like a battery?  In what way(s) is it different?
  18. 18. + Capacitance  How would capacitance change if the metal plates had more surface area?  Capacitance would increase.  How would it change if they were closer together?  Capacitance would increase.
  19. 19. + Dielectrics  The space between the plates is filled with a dielectric.  Rubber, waxed paper, air  The dielectric increases the capacitance.  Theinduced charge on the dielectric allows more charge to build up on the plates.
  20. 20. + Capacitor Applications  Connecting the two plates of a charged capacitor will discharge it.  Flash attachments on cameras use a charged capacitor to produce a rapid flow of charge.  Some computer keyboards use capacitors under the keys to sense the pressure.  Pushingdown on the key changes the capacitance, and circuits sense the change.
  21. 21. + Energy and Capacitors  Asthe charge builds, it requires more and more work to add electrons to the plate due to the electrical repulsion.  The average work or PE stored in the capacitor is (1/2)Q V.  Derive equivalent equations for PEelectric by substituting:Q= C V and V = Q/C
  22. 22. + ???? Classroom Practice Problem  A 225 F is capacitor connected to a 6.00 V battery and charged. How much charge is stored on the capacitor? How much electrical potential energy is stored on the capacitor?  Answers: 1.35 x 10-3 C , 4.05 x 10-3 J
  23. 23. + Now what do you think?  Ifa light bulb replaced the two metal plates and the battery was connected, electrons would flow out of the negative and into the positive terminal. Will this also occur with the two metal plates?  If not, why not?  If so, is the flow similar or different from that with the light bulb? Explain.
  24. 24. + 17.3 Current and Resistance Pg 608-617
  25. 25. + What do you think? • The term resistance is often used when describing components of electric circuits. • What behavior of the components does this term describe? • Do conductors have resistance? • If so, are all conductors the same? Explain. • What effect would increasing or decreasing the resistance in a circuit have on the circuit?
  26. 26. + Electric Current  Electric current (I) is rate at which charges flow through an area.  SI unit: coulombs/second (C/s) or amperes (A) 1A= 6.25 1018 electrons/second
  27. 27. + Conventional Current  Conventional current (I) is defined as the flow of positive charge.  The flow of negative charge as shown would be equivalent to an equal amount of positive charge in the opposite direction.  In conducting wires, I is opposite the direction of electron flow.
  28. 28. + Resistance to Current  Resistance is opposition to the flow of charge.  SI unit: volts/ampere (V/A) or ohms ( )  Ohm’s Law : V = IR  Valid only for certain materials whose resistance is constant over a wide range of potential differences
  29. 29. + Classroom Practice Problems  A typical100 W light bulb has a current of 0.83 A. How much charge flows through the bulb filament in 1.0 h? How many electrons would flow through in the same time period?  Given:  I= 0.83A t= 1 hour= 3600 seconds  Q= ?? C electrons= ??
  30. 30. + Classroom Practice Problems  I= Q/t or Q= It  Q= (0.83)(3600)  2988 C  We know that 1 A = 6.25 1018 electrons/second  2988 C x (6.25 x 1018 electrons/C)  1.87 x 1022electrons
  31. 31. + Classroom Practice Problems  This same 100 watt bulb (from the previous question) is connected across a 120 V potential difference. Find the resistance of the bulb.  Given:  V= 120V I= 0.83A R= ?? Ω R = V/I  120 V / 0.83 A  144.6
  32. 32. + Resistance of a Wire  On the next slide, predict the change necessary to increase the resistance of a piece of wire with respect to:  Length of wire  Cross sectional area or thickness of the wire  Type of wire  Temperature of the wire
  33. 33. +
  34. 34. + Applications  Resistors in a circuit can change the current.  Variableresistors (potentiometers) are used in dimmer switches and volume controls.  Resistors on circuit boards control the current to components.  Thehuman body’s resistance ranges from 500 000 (dry) to 100 (soaked with salt water).  Currents under 0.01 A cause tingling.  Currents greater than 0.15 A disrupt the heart’s electrical activity.
  35. 35. + Now what do you think? • The term resistance is often used when describing components of electric circuits. • What behavior of the components does this term describe? • Do conductors have resistance? • If so, are all conductors the same? Explain. • What effect would increasing or decreasing the resistance in a circuit have on the circuit?
  36. 36. + 17.4 Electric Power Pg. 618-623
  37. 37. + What do you think? • Hair dryers, microwaves, stereos, and other appliances use electric power when plugged into your outlets. • What is electric power? • Is electric power the same as the power discussed in the chapter “Work and Energy?” • Do the utility companies bill your household for power, current, potential difference, energy, or something else? • What do you think is meant by the terms alternating current (AC) and direct current (DC)? • Which do you have in your home?
  38. 38. + Types of Current - Direct  Batteriesuse chemical energy to give electrons potential energy.  There is a potential difference across the terminals  Chemical energy is eventually depleted.  Electrons always flow in one direction.  Called direct current (DC)
  39. 39. + Types of Current - Alternating  Generators change mechanical energy into electrical energy.  Falling water or moving steam  Electrons vibrate back and forth.  Terminals switch signs 60 times per second (60 Hz).  Called alternating current (AC)  AC is better for transferring electrical energy to your home.
  40. 40. + Energy Transfer  Is the electrical potential energy gained, lost, or unchanged as the electrons flow through the following portions of the circuit shown:  A to B  B to C  C to D  D to A  Explain your answers.
  41. 41. + Energy Transfer  A to B (unchanged)  B to C (lost in bulb)  C to D (unchanged)  D to A (gained in battery)
  42. 42. + Electric Power Click below to watch the Visual Concept. Visual Concept
  43. 43. + Electric Power  Power is the rate of energy consumption ( PE/ t ). For electric power, this is equivalent to the equation shown below.  SI unit: joules/second (J/S) or watts (W)  Current (I) is measured in amperes (C/s).  Potential difference ( V) is measured in volts (J/C).  Substitute using Ohm’s law ( V = IR) to write two other equations for electric power.
  44. 44. + Classroom Practice Problems  A toasteris connected across a 120 V kitchen outlet. The power rating of the toaster is 925 W.  What current flows through the toaster?  Given:  V= 120v P= 925W I= ??A I = P/ V  925 W / 120 V  7.7 A
  45. 45. + Classroom Practice Problems  What is the resistance of the toaster?  V= 120v I= 7.7A R= ?? R = V/I  120 V/ 7.7 A  16
  46. 46. + Classroom Practice Problems  How much energy is consumed in 75.0 s?  Energy =P t  P= 925 W t= 75 sec Energy=??  (925 W)(75.0 s)  6.94 104 J
  47. 47. + Household Energy Consumption  Power companies charge for energy, not power.  Energy consumption is measured in kilowatt•hours ( kw•h).  The joule is too small.  A kw•h is one kilowatt of power for one hour.  Examples of 1 kw•h:  10 light bulbs of 100 W each on for 1 h  1 light bulb of 100 W on for 10 h 1 kw•hr = 3 600 000 J or 3.6 x 106 J
  48. 48. + Electrical Energy Transfer  Transfer of energy from power plants to your neighborhood must be done at high voltage and low current.  Power lost in electrical lines is significant.  P = I2R  Power lines are good conductors but they are very long.  Since power companies can’t control the resistance (R), they control the current (I) by transferring at high voltage.
  49. 49. + Now what do you think?  Hair dryers, microwaves, stereos, and other appliances use electric power when plugged into your outlets.  What is electric power?  Is electric power the same as the power discussed in the chapter “Work and Energy?”  Do the utility companies bill your household for power, current, potential difference, energy, or something else?  What do you think is meant by the terms alternating current (AC) and direct current (DC)?  Which do you have in your home?
  50. 50. + NOT NEEDED??? Gravitational Potential Difference  Suppose a mass of 2.00 kg is moved from point A straight up to point B a distance of 3.00 m. Find the PEg for the mass if g = 9.81 m/s2. Repeat for a mass of 5.00 kg.  Answer: 58.9 J and 147 J  What is the PEg per kg for each?  Answer: 29.4 J/kg for both  The change per kg does not depend on the mass. It depends only on points A and B and the field strength.  There is an analogous concept for electrical potential energy, as shown on the next slide.
  • rosylyn

    Aug. 2, 2018
  • lim_cirilo

    May. 31, 2015

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