Chapter 5  electricity and magnestism
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Chapter 5 electricity and magnestism

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  • You will know the answers to these questions and have a better understanding of electricity and magnetism when you are done this unit
  • Discuss the fact that the North Pole is actually a South Pole!!!!!
  • Make an electomagnet!! Wrap wire around a metal tube and then test with a compass once the current is hooked up.
  • Notes
  • Show them that salt granules do not conduct only salt in an aqueous state can conduct.Water from our tap, is already an electrolytic solution. Find some distilled water. Test sugar as well
  • Lab 38??Show them our electroscope
  • Humid air has less static electricity.Try patting the cat!!!Dryer sheet help reduce static…sometimes..
  • Lab 39Why can’t the positive charges be moved? They are in the nucleus while electrons are in orbit outside
  • Who loses and who gains electrons depends on who is rubbed. Check the chart –do not memorize.Get out the static kit and have some fun. Do not forget the wand and a balloon.
  • Dynamics means Characterized by constant change, activity, or progress. A force that stimulates change or progress within a system or process.Show them a battery and how conventional current should flow Remember, the protons, positive charges, are in the nucleus. They do not actually move. The electrons move and they really go from negative to positive.
  • Series means in the same loop.Show them an actual series circuit.
  • Volts will thrill you, amps will kill you!!. It takes 100 mA to stop a heart. But volts and amps are tied together so beware.
  • Show a voltmeter and how it is hooked up in parallel. Show how to connect around what you want to determine the volts in.
  • This is a useful and important formula.They need practice problems on this section.
  • Lab 41 and 42 before next section??
  • Think of broken power lines.
  • Old version of Christmas tree lights were set up this way so when one burned out they all turned off and you had to check each bulb!!
  • Set up a circuit and show how the lights dim
  • Show this using an actual circuit
  • Show them the circuit we made a long time ago..it shows uaeful component
  • Note the simple loop. The positive and negative are indicated. Current flows from positive to negative – this is conventional current not electron flow. Electrons would not flow to a negative terminal.
  • Check the lab for some magnetite
  • Show using magnets that they attract and repelDo Lab 44.
  • They need to see a horseshoe magnet.
  • This is not a required section but magnetizing a nail is cool and fun. Let them try it. Or do the Steve Spangler Compass.
  • See if there are small compasses and show them the device. Turn the current on and off.
  • Conventional current is not the same direction as electron flow. It is the direction positive electrons would want to flow. They are attracted to the negative pole.
  • Show them the solenoid. Use the compasses to show the field.Use iron filings on glass as well.Show the correct position and have them practice this…Lab 46 -47
  • These are the factors that make them effective electromagnets----- Meeting Notes (12-01-30 12:18) -----As far as here on Monday
  • Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment, as well as being employed as industrial lifting electromagnets for picking up and moving heavy iron objects like scrap iron
  • Lab 48Work on sheets

Chapter 5 electricity and magnestism Presentation Transcript

  • 1. ELECTRICITY AND MAGNETISM Chapter 5 – The Material World
  • 2.  Look at the picture on page 138-139. Read the information on page 138.
  • 3. Circa 585 1600 Discovery of Discovery of magnetite, a the Earth’snatural magnet Circa 1120 magnetic Use of the compass fields for navigation
  • 4. 1752 1785 1672 Discovery Formulation of theConstruction of of electricala machine that Coulomb’s nature ofgenerates static Law light electricity
  • 5. 1821 1820 Invention 1827 Invention of the Formulation of the first of Ohm’s electro- Law electric 1800 magnet motorInvention of the electric cell(battery)
  • 6. 1882Construction, in NewYork, of first 2003 electrical distribution Construction 1986 of a a maglev network train in China Discovery of a ceramic super- conductor
  • 7. 1 - WHAT IS ELECTRICITY? Many natural phenomena are electrical in nature. 1. Nerve impulses 2. Bolts of lightening 3. Chemical reactions between atoms and molecules Electricity is one of the main forms of energy that powers the machines we use every day. Electrical phenomena were discovered a long time ago. The property of amber to attract small objects when it was rubbed with wool was called the electrical effect.
  • 8. Any material that can attract small objects after being rubbed is said to be electrically charged.Electrically charged objects can be attracted or repelled.Benjamin Franklin determined there were two types of charges: negative or positive.Electricity describes all the phenomena caused by positive and negative charges.
  • 9. 1.1 ELECTRICAL CHARGESProtons have a positive charge.Electrons have a negative charge.Protons are contained in the nucleus.Electrons are found orbiting the nucleus.The electrons found in the outermost shell (orbit) are the valence electrons.Valence electrons can be transferred to other atoms.
  • 10. If an object has more electrons than protons it is negatively charged.If an object has more protons than electrons it is positively charged.The Coulomb (C) is the unit of measurement for electric charge.One Coulomb is equal to the charge of 6.25 X 10 18 electrons or protons.The elementary charge is the charge carried by a single electron or proton. It has a value of 1.602 X 10 -19 C.
  • 11. ELECTRICAL FORCES OF ATTRACTION AND REPULSION Like charges repel. Opposites attract. The force at work during attraction and repulsion is the electrical force. Electrical charges can be neither created nor destroyed: only transferred. This is the Law of Conservation of Charge.
  • 12. 1.2 CONDUCTORS AND INSULATORS Most objects are electrically neutral. Transferring electrons can create a charge. Charging an object means creating an imbalance in the charges. Objects can be classified in three categories: 1. Conductors 2. Semi-conductors 3. Insulators
  • 13. Electrolytic solutions conduct electric current.A substance that conducts electricity when dissolved in an aqueous solution is called an electrolyte.Acids, bases and salts are electrolytes when in solution.  Salt in distilled water!!
  • 14. The role of water in electrolytic solutions.Pure, distilled water is not an electrolyte.The formula is H2O and this does not break into H+ and O2- when in solution!!Tap water has dissolved ions, such as salts and minerals from the environment.So tap water is often a very weak electrolyte.
  • 15. A substance that does not conduct electricity when dissolved in an aqueous solution is a nonelectrolyte.Organic compounds often fall into this category.C, H, and O compounds are often indicators of organic compounds.Sugar is C6H12O6!! Sugar in distilled water.
  • 16. Conductors permit the flow of electrical charges (electrons).Metals and electrolytic solutions are conductors.Insulators do not permit the flow of electrical charger (electrons).Nonmetals are usually insulators; wood, plastic, glass, ceramic, rubber, silk, and air.Semiconductors may be conductors or insulators, depending on other factors.Metaloids and carbon are semiconductors
  • 17. IDENTIFYING ELECTROLYTES!!!Acids, bases and salts conduct electricity when dissolved into a solution.How can we tell them apart?By their formulas!!
  • 18. SALTSSalts are made of a metal and a nonmetal OR a nonmetal and a group of atomsNaClCaCl2 KClMgCl2KINH4Cl
  • 19. BASESBases contain hydroxide (-OH) and a metal OR hydroxide combined with NH4NaOHKOHCa(OH)2Ba(OH)2NH4OH
  • 20. ACIDSThe formula usually begins with HThis is attached to a nonmetal or a group of atomsHClH3BO3H2SO4HBrH3PO4
  • 21. Organic acids are acids too.Citric acid – C5H7O5COOHThe H is added at the end of the formula
  • 22. 1.3 ELECTRICAL FIELDSElectrical charges interact with each other.Electrical forces can act on each other “at a distance”, meaning they do not have to contact/touch each other.An electric field is the area of space in which the electrical force of a charged body can act on another charged body.
  • 23. Electrical fields are invisible.They can be represented by electric field lines.Electric field lines show the direction of the force.They travel from positive(+) to negative (-).Opposites attract; likes repel.
  • 24. 2 STATIC ELECTRICITYStatic electricity describes all the phenomena related to electric charges at rest.Also called electrostatic electricity.Electric charges in motion are called dynamic electricity
  • 25. Electrically charged particles do not remain permanently charged.Gradually lose their charge.Charges do not “disappear” they are simply transferred to other objects or to water in the air.Transfer of charges is called electrostatic discharge.An electrostatic charge is sometimes accompanied by a spark. The air has been heated up!!
  • 26. 2.1 CHARGING AN OBJECTThere are 3 ways to charge an object: 1. By friction 2. By conduction 3. By induction
  • 27. Charging by friction – rub two items together.One will pull electrons from the other, which reults in them having opposite charges.Chart on page 146 –those at the top tend to gain electrons from those lower down. Plastic Sulphur Gold Nickel. copper Hard rubber (ebonite) Wood, yellow amber, resin Cotton Paper Silk Lead Wool Glass
  • 28. Charging by Conduction – touching a charged object to a neutral object.There must be physical contact.When the originally charged object is removed, the newly charged object stays charged.
  • 29. Charging by Induction – no touchingA charged object is brought near a neutral object.This causes the charges on the neutral object to separate.It will return to a neutral charge as soon as the charged object is removed.If the neutral object has a conductor attached to it, some of the moved charges will be conducted away and then the object remains charged. Even when the charged object is removed.
  • 30. 1. Which of the following is moved duringelectricity?A. ElectronsB. ProtonsC. Neutrons
  • 31. 2.This shows the equipment needed forcharging by:A. FrictionB. ConductionC. Induction
  • 32. 3.This shows charging by:A. FrictionB. ConductionC. Induction
  • 33. 4.This shows charging by:A. FrictionB. ConductionC. Induction
  • 34. 1. Which of the following is moved duringelectricity?A. ElectronsB. ProtonsC. Neutrons
  • 35. 2.This shows the equipment needed forcharging by:A. FrictionB. ConductionC. Induction
  • 36. 3.This shows charging by:A. FrictionB. ConductionC. Induction
  • 37. 4.This shows charging by:A. FrictionB. ConductionC. Induction
  • 38. 3 - DYNAMIC ELECTRICITY Describes all the phenomena related to electrical charges in motion3.1 – ELECTRIC CURRENT This is the orderly flow of charges. Conventional current flows from the positive electrode to the negative electrode
  • 39. CURRENT INTENSITY - AMPS This is the number of charges (e-) that flow past a given point in an electrical circuit every second. Simply put, the flow of electrons. The symbol is I The unit is the ampere (amp)with the symbol A. IA = 1C 1s
  • 40.  The current intensity in a circuit can be determined by the following formula: I= q Δt I is the current intensity, (A) q is the charge (C) Δt is the time interval, (s)
  • 41.  An ammeter is used to measure current intensity. When connecting an ammeter in a circuit it is hooked up in series.
  • 42. POTENTIAL DIFFERENCE - VOLTS This is the amount of energy transferred between two points in an electric circuit. It is measured in volts 1V = 1 J 1C
  • 43.  Potential Difference is determined using this formula: V=E q V is the potential difference,V E is the energy transferred in joules, J q is the charge, C
  • 44.  A voltmeter is used to measure potential difference. A voltmeter is connected in parallel.
  • 45. RESISTANCE Resistors transform electrical energy into another form of energy  Thermal energy - heat  Mechanical energy – movement like turning, spinning…  Light  Sound Resistors are often included in circuits to allow the amount of electrical energy passing through a circuit to be controlled or reduced
  • 46.  Electrical Resistance is the ability of a material to hinder the flow of electric current. The factors that affect a materials ability to be a resistor are: 1. The nature of the substance 2. The length – longer wire is a better resistor 3. Diameter – thinner wires are better resistors 4. Temperature – warmer temperature means more resistance A good conductor ( poor resistor) is: SHORT, FAT, COLD AND COPPER
  • 47.  Resistance (R) is measured in ohms (Ω) 1 Ω = 1V 1A
  • 48. OHM’S LAW For a for a given resistance, the potential difference in an electrical circuit us directly proportional to the current intensity. This formula can be rearranged to find V, R and I.
  • 49. 3.2 ELECTRICAL POWER This is the amount of work an electrical device can perform per second. An electrical power of one watt works at one joule per second. 1W = 1 J 1s
  • 50.  The formula for electrical power is: PE = W Δt PE is the electrical power, W (watts) W is the work, J (joules) Δt is the time interval, s (seconds)
  • 51. The formula for electrical power is: PE = W ΔtPE is the electrical power in watts, WW is the work, joules, JΔt is the time interval, seconds, s
  • 52. Power can also be determined by the following: PE = VIV is the potential difference in volts, VI is the current intensity, amps , A
  • 53. The amount of electrical energy used by a device can be determined by multiplying it electrical power by the time.Electrical energy is measured in joules (J) 1 W * 1 s = 1 J/s * 1 J/s * 1 s =1JKilowatt hours are also used 1 kWh = 1000 W * 3600 s = 3 600 000 J
  • 54. The kilowatt hour is the unit used to calculate consumption for electricity bills.The following formula is used to describe the relationship between electrical power and electrical energy: E = PΔt E = electrical energy in joules (J) or kilojoules (kJ) P = electrical power in W or kW t = time in s or h
  • 55. Changing from joules to kilojoules: 1 J = 1000 kJ To change from joules to kilojoules divide by 1000; 2000 J = 2 kJ 180 J = 0.18 kJTo change from kilojoules to joules multiply by 1000; 50 kJ = 50 000 J 0.25 kJ = 250 J
  • 56. Remember there are 60 seconds in one minute.3 minutes would have… 3 * 60 = 180 sThere are 60 minutes in one hour. 60 * 60 = 3600 s in one hourHow many seconds in 2.5 hours? 60 * 60 * 2.5 = 9000 s
  • 57. Example : If a 100 W amplifier runs for 30 minutes,how energy does it consume?Answer:E = PtP = 100 Wt = 30 * 60 = 1800 s E = 100 * 1800 = 180 000 J or 180 kJ
  • 58. Since P = VI, the formula can also be written as E = VItThere will be occasions when this is handy.
  • 59. Example:How much energy is used in 1 hour by a motorwhose rating plate indicates 110 V and 2.0 A?Answer: E = VIt so…V = 110 VI = 2.0 At = 1 h = 60 * 60 = 3600 s E = 110 * 2 * 3600 = 792000 J
  • 60. 3.3 ELECTRICAL CIRCUITSFor charges to flow, there must be a loop for them to follow and they must be able to return to the startAn electrical circuit is a network in which electrical charges can flow continuously.The loop must be closed with no breaks.
  • 61. The lights will turn on as long as the switch is closed and there are no other breaks. What is a burned out light bulb?A break! In this case it will cause the electric current to stop and none of the lights will light.
  • 62. All electrical circuits have three things:1. A power supply2. One or more elements that use electrical energy3. Wires to carry the chargesWe use symbols to represent these and in our circuit diagrams
  • 63. SERIES CIRCUITS The elements are connected end to end and make a single loop. This means that if one of the parts of the circuit is defective, no current will pass so nothing will work. Energy is used up as it passes along, so the last element may not receive much!!!
  • 64. PARALLEL CIRCUITSA circuit that branches at least onceThe current may follow different pathsIf one branch has a defective component the other branches will not be prevented from working.The total current is divided at the branches; not always equally.The voltage will be the same in eachbranch
  • 65. In a series circuit the number of amps is the same at every point along the way. It = I1 = I2 = I3 = I4…In a series circuit the number of volts is divided over the components using the circuit. Vt = V1 + V2 + V3 + V4…Since your voltage is not the same everywhere your lights will not be equally bright!!
  • 66. It=5A I1=5A I2=5A I3=5A Vt=15A V1= 5A V2= 5A V3= 5A The volts only split evenly if the bulbs are equal in resistance
  • 67. In parallel circuits, voltage is equal in each branch Vt = V1 = V2 = V3 = V4…In parallel circuits the amps (current is divided) but not always evenly. It = I1 + I2 + I3 + I4…Bulbs on different branches will have the same brightness!!
  • 68.  Power supplies are the cell or battery The switch is a switch!! Resistor (anything that slow current down and uses energy – lights, motors, actual resistors…) The lamp is a light bulb but they can also be represented by the resistor symbol
  • 69. The bulbs can be represented by resistorssymbol, as well.
  • 70. Draw a series circuit with the following elements: a switch, a power supply, 2 resistors, an ammeter and a voltmeter. The voltmeter is measuring the voltage over one of the light bulbs.
  • 71.  Draw a series circuit diagram which has the following elements: a switch, a battery, 3 light bulbs, a resistor, an ammeter and a voltmeter. The voltmeter is to measure the voltage over the battery.
  • 72. Draw a series circuit with 2 resistors and 2 light bulbs, a power supply and a switch. Include an ammeter and a voltmeter. The voltmeter is measuring the potential difference over the two resistors.
  • 73. Draw a parallel circuit with the following elements: one power supply, one switch, 3 light bulbs in parallel with each other and an ammeter to measure the current in the circuit.
  • 74. Draw a parallel circuit with the following elements: a switch, a power supply, two light bulbs, 2 ammeters and 2 voltmeters. The amps and volts must be measured in each bulb.Do we need two voltmeters?????
  • 75. WHAT IS MAGNETISM?A magnet is an object that can attract other objects containing iron, cobalt and nickel.Magnetism describes all the phenomena caused by magnets.
  • 76. MAGNETIC FORCES OF ATTRACTION AND REPULSION All magnets have a north-seeking and a south- seeking pole The N-pole of a magnet is attracted to the North pole of the Earth This means that the magnetite north pole is really a south pole!!! Opposite magnetic poles attract. Like magnetic poles repel
  • 77. 4.2 MAGNETIC FIELDSThis is the area of space in which the magnetic force of a magnet can act on another magnet.Iron, nickel or cobalt can all be made into magnets so they are affected by the magnetic field.
  • 78. Magnetic field lines go from the north pole to the south pole.The lines are closer together at the poles where the force is greater
  • 79. 4.3 MAGNETIZING OBJECTSA ferromagnetic substance is a substance with the ability to acquire magnetic propertiesThe items must contain some iron, nickel or cobalt.We must line up the domains!!!Can be done with a strong magnet moving correctly.Can also be done using electricity, which we will see laterA magnet can be demagnetized by a sharp hit, too much heat, or the presence of the opposite pole
  • 80. 5 - ELECTROMAGNETISMElectromagnetism describes all the phenomena resulting from the interaction between electricity and magnetism.
  • 81. 5.1 MAGNETIZATION BY ELECTRICITYA magnetic field can be generated using dynamic electricity.The magnetic field will only exist when the current flows.The Magnetic field of a live wire:The magnetic field lines form circles around the wire.Their direction depends on the current direction
  • 82. THE RIGHT-HAND RULEThe thumb points in the direction of conventional current (points to the negative pole) and the curve of the fingers show the direction of the magnetic field lines (point towards the south pole)
  • 83. AN ASSIGNMENT TO BE DONE IN TEAMSAND DONE IN 5 MINUTES.Create a solenoid.Explain, in writing, what you have done and what you can expect from your solenoid. Be sure to explain if the nail is important
  • 84. THE MAGNETIC FIELD OF A SOLENOIDA solenoid is a cylindrical coil of live wire.The magnetic field of a solenoid is stronger than the electric field of a straight conductor (straight wire)Again, use your right hand!!The curved fingers point in the direction of conventional current.The thumb points to the north
  • 85. The core used in a solenoid can make the fieldstronger –soft iron cores are most effective.The more coils the solenoid has the stronger thefield.More current makes a stronger current too.
  • 86. HOW IS A SOLENOID DIFFERENT FROM A BARMAGNETThe magnetic field of a solenoid can be turned on and offThe direction of the magnetic field can be reversed by changing the direction of the current.The strength (intensity) can be modified by adjusting the electric current.The strength of a bar magnet can not be modified at will.
  • 87. These characteristics of solenoids explain why they are used in technological applications.And they can easily be turned into electromagnets
  • 88. 5.2 CHARGING BY MAGNETISMCan electric current be generated from a magnetic field?Yes!!The magnetic field must be in motion relative to the charge or the conductor.Two ways to do this:  By moving a conductor inside a magnetic field  By moving a magnet around a conductor
  • 89. Electromagnet induction means generating a electric current in a conductor by varying a magnetic field around the conductor.It is used to transform mechanical energy into electrical energyMost electric generators work this way. Electromagnetic induction Steve Spanglers Electromagnet