1.ELECTRICITY AND MAGNETISM Chapter 5 The Material World

2. Look at the pictureon page 138-139. Read the informationon page 138. 3. Circa 585 1600 Discovery of Discovery of magnetite, athe Earthsnatural magnet Circa 1120magnetic Use of the compass fields for navigation 4. 1752 1785 1672DiscoveryFormulation of theConstruction of of electricala machine that Coulombs nature ofgenerates static Lawlightelectricity 5. 1821 1820Invention1827Inventionof theFormulationof the first of Ohms electro- Law electric1800 magnetmotorInventionof the electric cell(battery) 6. 1882Construction, in NewYork, of first 2003electrical distributionConstruction 1986 of a a maglevnetworktrain 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 thatpowers the machines we use every day. Electrical phenomena were discovered a long timeago. The property of amber to attract small objectswhen it was rubbed with wool was called theelectrical 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 CHARGESProtons 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 REPULSIONLike 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. SALTSSalts are made of a metal and a nonmetal OR a nonmetal and a group of atomsNaClCaCl2 KClMgCl2KINH4Cl 19. BASESBases contain hydroxide (-OH) and a metal OR hydroxide combined with NH4NaOHKOHCa(OH)2Ba(OH)2NH4OH 20. ACIDSThe formula usually begins with HThis is attached to a nonmetal or a group of atomsHClH3BO3H2SO4HBrH3PO4 21. Organic acids are acids too.Citric acid C5H7O5COOHThe H is added at the end of the formula 22. 1.3 ELECTRICAL FIELDSElectrical 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 ELECTRICITYStatic 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 OBJECTThere are 3 ways to charge an object:1. By friction2. By conduction3. 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.PlasticSulphurGold Nickel. copper Hard rubber (ebonite)Wood, yellow amber, resin Cotton PaperSilkLead 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 touchingA 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 thenegative electrode 39. CURRENT INTENSITY - AMPS This is the number of charges (e-) that flow past a givenpoint 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 thefollowing formula: I= q t I is the current intensity, (A) q is the charge (C) t 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 inseries. 42. POTENTIAL DIFFERENCE - VOLTS This is the amount of energy transferred between twopoints in an electric circuit. It is measured in volts 1V = 1 J 1C 43. Potential Difference is determined using this formula:V=Eq 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 ofenergy Thermal energy - heat Mechanical energy movement like turning, spinning Light Sound Resistors are often included in circuits to allow the amountof electrical energy passing through a circuit to becontrolled or reduced 46. Electrical Resistance is the ability of a material to hinderthe flow of electric current. The factors that affect a materials ability to be a resistorare: 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 () 1 = 1V 1A 48. OHMS LAW For a for a given resistance, the potential difference in anelectrical circuit us directly proportional to the currentintensity. 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 performper second. An electrical power of one watt works at one joule persecond.1W = 1 J 1s 50. The formula for electrical power is: PE = Wt PE is the electrical power, W (watts) W is the work, J (joules) t is the time interval, s (seconds) 51. The formula for electrical power is: PE = WtPE is the electrical power in watts, WW is the work, joules, Jt 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=1JKilowatt 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 = Pt 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 have3 * 60 = 180 sThere are 60 minutes in one hour. 60 * 60 = 3600 s in one hourHow 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 soV = 110 VI = 2.0 At = 1 h = 60 * 60 = 3600 sE = 110 * 2 * 3600= 792000 J 60. 3.3 ELECTRICAL CIRCUITSFor charges to flow, there must be a loop for them to follow and they must be able to return to the startAn 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 chargesWe use symbols to represent these and in ourcircuit diagrams 63. SERIES CIRCUITS The elements are connected end to end and make a singleloop. 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 maynot receive much!!! 64. PARALLEL CIRCUITSA circuit that branches at least onceThe current may follow different pathsIf one branch has a defective component the otherbranches will not be prevented from working.The total current is divided at the branches; notalways 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 = I4In a series circuit the number of volts is divided over the components using the circuit.Vt = V1 + V2 + V3 + V4Since your voltage is not the same everywhere your lights will not be equally bright!! 66. It=5AI1=5A I2=5AI3=5A Vt=15AV1= 5AV2= 5AV3= 5AThe volts only split evenly if the bulbsare equal in resistance 67. In parallel circuits, voltage is equal in each branchVt = V1 = V2 = V3 = V4In parallel circuits the amps (current is divided) butnot always evenly. It = I1 + I2 + I3 + I4Bulbs on different branches will have the samebrightness!! 68. Power supplies are the cellor battery The switch is a switch!! Resistor (anything that slowcurrent down and usesenergy lights, motors,actual resistors) The lamp is a light bulb butthey can also be representedby 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 followingelements: a switch, a battery, 3 light bulbs, a resistor, anammeter and a voltmeter. The voltmeter is to measure thevoltage 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 Northpole of the Earth This means that the magnetite north pole is really asouth pole!!! Opposite magnetic poles attract. Like magnetic poles repel 77. 4.2 MAGNETIC FIELDSThis 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 OBJECTSA ferromagnetic substance is a substance with the ability to acquire magnetic propertiesThe 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 laterA magnet can be demagnetized by a sharp hit, too much heat, or the presence of the opposite pole 80. 5 - ELECTROMAGNETISMElectromagnetism describes all the phenomena resulting from the interaction between electricity and magnetism. 81. 5.1 MAGNETIZATION BY ELECTRICITYA 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 RULEThe 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 SOLENOIDA 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 BARMAGNETThe magnetic field of a solenoid can be turned on and offThe 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 MAGNETISMCan 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 energyMost electric generators work this way. Electromagnetic induction Steve Spanglers Electromagnet