Chapter 5 electricity and magnestismPresentation Transcript
ELECTRICITY AND MAGNETISM Chapter 5 – The Material World
Look at the picture on page 138-139. Read the information on page 138.
Circa 585 1600 Discovery of Discovery of magnetite, a the Earth’snatural magnet Circa 1120 magnetic Use of the compass fields for navigation
1752 1785 1672 Discovery Formulation of theConstruction of of electricala machine that Coulomb’s nature ofgenerates static Law light electricity
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)
1882Construction, in NewYork, of first 2003 electrical distribution Construction 1986 of a a maglev network train in China Discovery of a ceramic super- conductor
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.
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.
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.
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.
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.
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
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!!
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.
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.
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
IDENTIFYING ELECTROLYTES!!!Acids, bases and salts conduct electricity when dissolved into a solution.How can we tell them apart?By their formulas!!
SALTSSalts are made of a metal and a nonmetal OR a nonmetal and a group of atomsNaClCaCl2 KClMgCl2KINH4Cl
BASESBases contain hydroxide (-OH) and a metal OR hydroxide combined with NH4NaOHKOHCa(OH)2Ba(OH)2NH4OH
ACIDSThe formula usually begins with HThis is attached to a nonmetal or a group of atomsHClH3BO3H2SO4HBrH3PO4
Organic acids are acids too.Citric acid – C5H7O5COOHThe H is added at the end of the formula
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.
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.
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
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!!
2.1 CHARGING AN OBJECTThere are 3 ways to charge an object: 1. By friction 2. By conduction 3. By induction
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
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.
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.
1. Which of the following is moved duringelectricity?A. ElectronsB. ProtonsC. Neutrons
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
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
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)
An ammeter is used to measure current intensity. When connecting an ammeter in a circuit it is hooked up in series.
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
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
A voltmeter is used to measure potential difference. A voltmeter is connected in parallel.
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
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
Resistance (R) is measured in ohms (Ω) 1 Ω = 1V 1A
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.
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
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)
The formula for electrical power is: PE = W ΔtPE is the electrical power in watts, WW is the work, joules, JΔt is the time interval, seconds, s
Power can also be determined by the following: PE = VIV is the potential difference in volts, VI is the current intensity, amps , A
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
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
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
Remember there are 60 seconds in one minute.3 minutes would have… 3 * 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
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
Since P = VI, the formula can also be written as E = VItThere will be occasions when this is handy.
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
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.
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.
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 our circuit diagrams
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!!!
PARALLEL CIRCUITSA circuit that branches at least onceThe current may follow different pathsIf 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
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!!
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
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!!
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
The bulbs can be represented by resistorssymbol, as well.
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.
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.
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.
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.
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?????
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.
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
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.
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
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
5 - ELECTROMAGNETISMElectromagnetism describes all the phenomena resulting from the interaction between electricity and magnetism.
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
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)
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
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
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.
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.
These characteristics of solenoids explain why they are used in technological applications.And they can easily be turned into electromagnets
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
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