The Energy Challenge – Electricity

Forms of Energy Energy comes in many forms from many different sources. Some examples are: – Electrical energy - movement of electrons between atoms – Thermal energy - movement of particles within a substance – Radiation energy - energy of electromagnetic waves – Chemical energy – energy stored in chemical bonds

Forms of Energy – Wind energy – movement of air – Hydraulic energy – movement of water

Transformation of Energy Energy is constantly converted from one form to another Wind, hydraulic, radiation (solar) and geothermal energy can all be converted to electrical energy. Electrical energy from a circuit can be converted into the radiation (light) energy of a light bulb or the thermal energy of a furnace

Law of Conservation of Energy During these transformations, energy can be neither created nor destroyed. The total amount of energy always remains constant

Electrical Charge All matter contains charges: Positive charges from its protons Negative charges from its electrons A substance is said to be charged if its positive and negative charges are not balanced A substance has a negative charge if it has gained electrons and has more electrons than protons A substance has a positive charge if it has lost electrons and has more protons than electrons

Electrical Charge Substances that have a like charge repel each other Substances that have an opposite charge attract each other

Electrical Charge When two electrically neutral (balanced + and – charges) rub against each other, the friction can cause electrons to move from one to the other When a charged object touches an electrically neutral object, it can transfer its charge In some cases, a charged object can even transfer its charge just by being near a neutral object

Static Electricity Electrostatic series TendencySubstance Tend to gain electronsRubber Ebonite Polyethylene (vinyl) Cotton Silk Wool Glass Acetate Tend to give up electronsCat’s Fur

Static Electricity When you rub these together… Then you bring these together… This is the force you get (attract or repel) Ebonite & Rubber Wool & Glass Rubber & Glass Silk & Vinyl Acetate & Ebonite Silk & Acetate Cotton & Glass Cat’s Fur & Silk Cotton & Cat’s Fur Ebonite & Silk Cotton & Wool Wool & Ebonite Vinyl & Cotton Rubber & Glass Vinyl & Glass

Electrical Functions In an electric circuit, different parts perform a variety of functions The main functions are: Power supply – provides energy to make current flow (ex. batteries, electrical outlets)

Electrical Functions In an electric circuit, different parts perform a variety of functions The main functions are: Power supply – provides energy to make current flow (ex. batteries, electrical outlets) Conduction – carry the electrons through the circuit (wires) Insulation – cover wires to prevent shocks (plastic)

Electrical Functions Protection – devices that stop current flow in case of malfunction (fuses or circuit breakers)

Electrical Functions Protection – devices that stop current flow in case of malfunction (fuses or circuit breakers) Control – opens and closes to complete the circuit and control the flow of current through the circuit (switch)

Electrical Functions Protection – devices that stop current flow in case of malfunction (fuses or circuit breakers) Control – opens and closes to complete the circuit and control the flow of current through the circuit (switch) Transformation of energy – converts electrical energy to another form of energy (most devices and appliances)

Electrical Circuits When electrical charges are placed in a circuit made of conductive materials, electricity can flow in a loop Because electrons all have the same charge (-), they repel each other and push each other along from one atom to the next This movement is called electric current

Types of Current Alternating Current Electrons move back and forth many times per second ion?quick=oy&att= ion?quick=oy&att=1787 Direct Current Electrons continuously move in the same direction

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Electrical Circuits There are two kinds of electrical circuits: Series Circuits Parallel Circuits

Series Circuits All parts of the circuit are connected one after the other, so that the current can only follow one path

Parallel Circuits There is at least one branch in the circuit, so the current may follow different paths

Current Intensity ( I ) The number of electrons passing a point in a circuit per second can be measured This is called current intensity (represented by the letter I) Current intensity is measured in units called Amperes, or amps, represented by the letter A It is measured with a device called an ammeter, which must always be connected in series

Current Intensity

Voltage or Potential Difference (V) Voltage, represented by the symbol V, is a measurement of the amount of energy that can be supplied along a circuit Voltage is measured in units called Volts, which are also represented by the letter V Voltage is measured using a voltmeter, which must always be connected in parallel

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Connecting a Circuit

Drawing a Circuit Diagram ComponentDrawing Wire Power Supply/Battery + - Closed Switch Resistor Open Switch Ammeter Voltmeter Light Bulb A V

Draw the following: A circuit with a power supply, 3 light bulbs and a switch connected in series A circuit with a power supply and 3 light bulbs connected in parallel. Place a switch on it so all 3 lights will turn off if it is opened. Place a second switch on it that will only turn off one light if it is opened. Place an ammeter (labelled A 1 ) to measure current flowing through the whole circuit Place ammeters (labelled A 2, A 3, A 4 ) to measure current flowing through each light bulb

Draw the following: A circuit with a power supply, 2 lights in series and 1 light in parallel with the other two. Place a switch so that one light goes off. Place another switch so that two lights go off. Place another switch so that all lights go off. Place a voltmeter (V 1 ) to measure the voltage drop at the power supply Place voltmeters (V 2, V 3, V 4 ) to measure voltage drop over each light bulb

Resistance (R) In an electrical circuit, the force that slows down the flow of electrons is called RESISTANCE Resistance can be calculated using this formula: R = V I Resistance is measured in Ohms (Ω)

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Conductance (G) Conductance is the opposite of resistance, so it measures how well a substance or circuit allows electricity to flow through Conductance is calculated using the formula G = I V Conductance is measured in Siemens (S)

Factors affecting electrical conductivity (short, fat, cold, copper) Four factors determine how well a conductor will conduct electricity – Length A shorter wire conducts better than a longer wire – Diameter A thicker wire conducts better than a thinner wire

Factors affecting electrical conductivity (short, fat, cold, copper) – Temperature A colder wire will conduct better than a warmer wire – Material Certain materials are better conductors than others Copper is usually the best

My Formula Sheet (these will always be given to me) R = VG = I I V

My Life-Saver (I need to remember this) When measuring:The symbol is:And you measure in: VoltageVVolts (V) Current Intensity I Amps (A) ResistanceROhms (Ω) ConductanceGSiemens (S)

Electrical Power (P) The amount of work (how much energy it can transform in a period of time) is called electrical power Power (P) is calculated using this formula: P = IV Power is measured in Watts (W) or Kilowatts (kW) W ÷ 1000 = kW

My Formula Sheet (these will always be given to me) R = VG = I I V P = I V

My Life-Saver (I need to remember this) When measuring:The symbol is:And you measure in: VoltageVVolts (V) Current Intensity I Amps (A) ResistanceROhms (Ω) ConductanceGSiemens (S) PowerPWatts (W)

Relationship between Power and Energy Energy can be measured using two different units: kilowatt-hours (kWh) Joules (J)

Calculating Energy in kWh Convert the watts into kilowatts Multiply by the total number of HOURS Multiply by the cost per kilowatt-hour if the total cost is requested

Calculating Energy in Joules Use one of the two formulas below: E = V I t E = Pt In both, t stands for time (must be measured in seconds)

My Formula Sheet (these will always be given to me) R = VG = I I V P = I VE = V I t E = Pt

My Life-Saver (I need to remember this) When measuring:The symbol is:And you measure in: VoltageVVolts (V) Current Intensity I Amps (A) ResistanceROhms (Ω) ConductanceGSiemens (S) PowerPWatts (W) EnergyEJoules (J) Or Kilowatt-hours (kWh) Timetseconds (s) Or hours (h)

Energy Efficiency During any transformation of energy, only a certain amount of the total energy is actually used. The rest is changed into another form or “lost” outside of the system. Ex. A light bulb only uses 5% of the electrical energy it consumes to produce light. The rest is lost as heat energy. Energy efficiency (%) is calculated using the following formula: Quantity of energy used (usable or useful) x 100 Quantity of energy consumed

Magnetism Discovered in the ancient Greek region of Magnesia, a substance named magnetite was the first known magnet Magnets have certain properties: They can attract or repel other magnets They can attract ferromagnetic substances

Magnets Magnets behave as they do because they have permanently aligned “magnetic domains”

Ferromagnetic Substances Ferromagnetic substances have certain properties: They are attracted to magnets They can become temporarily magnetized, because they also have magnetic domains Three substances are considered ferromagnetic: iron, nickel and cobalt

Non-Magnetic Substances Non-magnetic substances are not attracted to magnets because they have no magnetic domains

Magnetic Fields Magnetic fields always exist around magnets These fields have a shape and a direction that can be represented by lines of force By convention, these lines of force always go from north to south poles

Forces of Attraction and Repulsion All magnets have two poles: a north pole and a south pole When magnets are brought near one another, they affect one another’s magnetic fields: Like (same) poles will repel each other Opposite poles will attract

Forces of Attraction and Repulsion

Magnetic Fields

Electromagnetism The movement of electricity also generates magnetic fields The shape and direction of the field depends upon the direction of the flow of current In a straight wire, we use the right hand rule to determine both shape and direction Another kind of electromagnet is a SOLENOID in which conductive wire is wrapped around a core

Right Hand Rule Point your thumb in the direction of the flow of conventional current through the wire (+ to -) Your fingers holding the wire show you the shape and direction of the magnetic field

Electromagnets Electromagnets have a major advantage that they can be turned on and off They also have many practical uses MRI machines in medicine Burglar alarms in homes Metal detectors in airports Microphones, speakers, headphones, doorbells…