Electricity Static Currents Circuits Electricity l l l

Electricity Static, Currents, Circuits

Electricity? l l l Electricity is all about electrons, which are the fundamental cause of electricity Static Electricity - involves electrons that are moved from one place to another, usually by rubbing or brushing Current Electricity - involves the flow of electrons in a conductor

Electricity Everything in the world is made up of atoms. Each atom has smaller parts in it. One of those parts is called electrons. Electrons can move from atom to atom. When an electron moves to a different atom, it causes another electron to have to move. When electrons move quickly from one atom to another is it called Electricity!

Let Us Review l ATOMS………………….

Atoms… l Have neutrons, protons, and electrons. l Protons are positively charged l Electrons are negatively charged

Electrons… l Are located on the outer edges of atoms…they can be moved. l A concentration of electrons in an atom creates a net negative charge. l If electrons are stripped away, the atom becomes positively charged.

The world is filled with electrical charges: + - + + + + + -

What is this electrical potential called? l Static - Electricity - - - + ++ ++

Static Electricity l The build up of an electric charge on the surface of an object. l The charge builds up but does not flow. l Static electricity is potential energy. It does not move. It is stored. l When static electricity is discharged a “spark” or “shock” occurs.

Static electricity is caused when certain materials are rubbed against each other. l Electrons can be rubbed off one material and on to another. l The material that has got extra electrons is now negatively charged l The material which has lost electrons is positively charged. l

Where do charges come from? Rubbing materials does NOT create electric charges. It just transfers electrons from one material to the other.

Where do charges come from? When a balloon rubs a piece of wool. . . + + – – – + + wool + electrons are pulled from the wool to the balloon. The balloon has more electrons than usual. The balloon: – charged, The wool: +charged

Static Discharge… l Occurs when there is a loss of static electricity due to three possible things: l. Friction - rubbing l. Conduction – direct contact l. Induction – through an electrical field (not direct contact)

Static Discharge Human body can not feel less than 2, 000 volts of static discharge Static charge built up by scuffing shoes on a carpet can exceed 20, 000 volts?

The Electrostatic Force l The electrostatic force is simply the field force that exerted by electrical charges l Because of the intensity of the attraction between charged atoms, it is stronger than the force of gravity

Static Electricity Static electricity is the charge that stays on an object. Law of Charges Unlike charges attract each other, and like charges repel each other.

Electrical Charge l Some materials have a weak affinity (attraction) for electrons so they easily loose their electrons due to friction. When you walk across the floor you pick up these electrons and become “charged”. When you touch someone you release that charge (discharge) and shock them.

Electrical Charge l Most objects are neutral because their charges are balanced, but when conditions change so do the electrical charges l Have you noticed how on drier days you seem to pick up charges more easily and can “shock” your friends easily?

Electrical Charge l The reason some materials seem to have more ability to cause “shock” is because some materials have a weaker affinity for electrons l They give up their electrons more easily l When you walk across carpet your shoes/socks are able to pick up the electrons because the carpet easily gives them up l The you can SHOCK your friends

Electrical Charge When an object loses electrons it becomes positive l A gain of electrons results in a negative charge l Whether a charge is negative or positive, the net charge is measured in Coulombs (C) l l One Coulomb is the charge carried by 6. 24 x 1018 protons or electrons

Electrical Charge l Remember insulators? l The reason they insulate so well is because they hold so tightly to their electrons (not allowing them to flow) l Conductors? l Conductors conduct so well because they hold loosely to their electrons allowing electrons to flow

Electric Fields l Electrostatic force is a field forcel Meaning that it is exerted over an area l Charged objects can exert a force on distant charges which they are not in direct contact l Physicists have noticed that electrical charges flow in a particular pattern l Lines of force radiate outward from a charged object through a path of least resistance

Electric Fields l The area around electric charges that has the force of the charge exerted on it. l When a charge is placed in an electric field, it is pulled or pushed. l The field is the strongest near the charged particle.

Electrical Induction l Is the creation of charge region when a neutral object when exposed to a nearby electrical charge l They do NOT touch l The charge is temporary l It is a field force

Electrical Induction • Dipole- contains a positive and a negative pole (end) • it is a neutral molecule whose electrons have shifted from positive to negative

Detecting Charges l Electroscope- an instrument used to detect the presence of a charge l They do NOT detect type of charge nor amount l It cannot quantify

Conductors vs. Insulators l Conductors – material through which electric current flows easily. l Insulators – materials through which electric current cannot move.

Transferring Charges l Electrical conductors- allow electricity to flow through, because they hold their electrons loosely l Most often these are metals l Remember l that sea of electrons Electrical insulators- do not allow electricity to flow, because they hold onto their electrons very tightly l Glass, wood, and rubber

Transferring Charges l Remember when you get rid of your stored electrons you are discharging the surface l Electrical discharge causes the shock you experience after a build up of static electricity

Transferring Charges l Semiconductors- allows limited electron flow or conduct under certain conditions l This is because some materials can change their electron affinity in response to environmental conditions

Examples l Conductors: l Metal l Water (only because of the minerals and metals in the water) l Insulators: l Styrofoam l Rubber l Plastic l Paper l Wood

Grounding What is grounding? An object is grounded when it is connected to the earth through a connecting wire. If a charged conductor is grounded, it will become neutral.

Grounding l Additional wire in circuit to protect a person from shock. l Plugs have a 3 rd prong. This connects the metal shell of the appliance to the ground wire of the building.

Lighting Rods l Lightning rods were used to protect buildings from lightning strikes l Lightning rod- metal rod mounted to the roof of a building. If lightning strikes the rod the energy flows down the rod to a ground wire and then into the Earth.

Storing Charges l How can we make an object keep its charge? l Remember insulators keep their electrons while conductors allow their electrons to flow freely……

Storing Charges l So… l To store a charge we must use both conductors and insulators…….

Storing Charges l Leyden jar- one of the first devices used to store charges l It is made of a jar (glass or plastic) lined and coated with lead and that used electrical induction and grounding to greatly increase storage capacity l Other metals will work, with less power

Storing Charges l Capacitors are devices used to store electrical energy today. l They are constructed very similarly to a Leyden Jar

How do we apply our knowledge of static electricity? l Pollution is a huge problem today, especially in big cities and in homes l Just like every other material even dust and other pollutants have atoms; and thus protons and electrons l Ionic purifiers clean the air by using electricity to attract and trap dust by generating negative ions. The negative ions are created by running high voltage electricity through thin metal plates that create a negative charge on surrounding gas molecules and adhere to the particulates in the air. Now that the particulates are linked with a negative charge, they are attracted to their opposite polarity, a positively charged metal plate that captures the impurities from the passing air flow.

Electrical Current and Ohm’s Law

Electricity that moves… l Current (electricity): The flow of electrons from one place to another. l Measured in amperes (amps) l Kinetic energy

Electrical Current Electrical potential energy is the ability to allow electricity to flow l Conventional current flow- the flow of positive charges through a conductor, this is opposite the flow of electrons l

Electrical Current l Conventional flow- flow of positive charges through a conductor l Let us look at this more. . l Now we know that protons do not move. This idea does not change that rule l What occurs when an electron leaves an atom, it leaves a positive hole. This causes an electron to move into it and another electron moves out in a different direction l So we can say that conventional current is movement of positive “holes” through a conductor

Current l The directed movement of electrons or the flow. (pushed by voltage) üUnit of measure is the amp or ampere üMeasured with an ammeter or amp meter

Conventional theory Says that current flows from + to Scientists first guessed that it was the proton that was in motion in the atom

Electron theory Says that current flows from – to + When scientists discovered that it was the electron that was in motion, electron theory was born

Does it matter? When talking about electronics, it does matter which way current flows, but for basic electricity, it doesn’t l Most automotive texts, and classes still teach conventional theory, so that is what we will stick with. l

Direct Current (DC) Flows in one direction, directly/straight from the source l Items such as: l l Cell phone l Digital camera l Laptop computer l Are powered by a direct current: because they have batteries

Direct Current: l Electrical circuit= Path through which electricity flows l Electrical load- takes the electrical energy and converts it to another form of energy l Light bulb- converts electrical energy to light energy

D. C. Current l Current always flowing the same way

Sources of a Direct Current l Electrochemical Cells and Batteries l An electrochemical cell uses electrons released by a chemical reaction l This chemical reaction occurs between a metal and electrolyte paste l. A battery consists of one or more electrochemical cells

Batteries contain one or more electric cells l Electric cell- a wire connects 2 metals that are in contact with an electrolyte, it uses chemical energy to produce an electrical current l l Electrolyte- a liquid or paste substance that conducts electricity

Batteries l l l Wet Cell- uses a liquid electrolyte to conduct electricity Dry Cell- uses a paste electrolyte to conduct electricity When a battery is “dead” it is because the metal in the battery no longer reacts with the electrolyte. l The electrolyte may be depleted or l The metal is used up

What is a generator? l Generator – a machine that changes mechanical energy to electrical energy l Usually use moving magnets to create currents in coils of wire.

Sources of Direct Current l Photovoltaic Cells- solar cells that use energy absorbed via light rays to power electrical devices l The light ray is absorbed by a semiconductor, its electrons then gain kinetic energy and jump about creating energy!

Alternating Current l The current electricity flows from a source through many conductors to several outlets l It periodically changes direction at a specific frequency

A. C. Current l Current flows first one way, then the other

Direct current versus alternating current – AC vs DC : What’s the difference? Direct current is electrical current which comes from a battery which supplies a constant flow of electricity in one direction. Alternating current is electrical current which comes from a generator. As the electromagnet is rotated in the permanent magnet the direction of the current alternates once for every revolution. .

How do we Measure Electricity? l Volt– the measurement of the amount of electrical push or force in a circuit l Watt– the measurement of power, or how fast work is done l Ampere– a unit used to measure how much current flows through a given part of a circuit in one second

What is Voltage? l The measure of energy given to the charge flowing in a circuit. l The greater the voltage, the greater the force or “pressure” that drives the charge through the circuit.

Voltage l A VOLT is the SI unit for potential difference l The difference in electrical potential between two points l The amount of work needed to move a charge between them l 1 V = 1 J 1 C

Voltage l Electrical pressure (pushes current) Atoms that are short electrons and atoms with extra electrons üUnit of measure is the volt üMeasured with a voltmeter Note! A good voltmeter won’t have any flow thru it

Ways to make voltage Magnets l Chemical l Pressure l Heat l Light l Friction l Most common

Calculating Volts If an electric motor operates at 2880 watts and 12 amps, what would be the voltage requirement for that motor? Volts = 2880 Watts / 12 Amps 2880 / 12 = 240 Volts

How much is one amp? l One amp is 6. 25 X 10 to the 18 th power of electrons past a given point per second. (one Coulomb) 6, 250, 000, 000

The Amp l SI unit of electrical current is the ampere (A) or amp l 1 A= 1 C 1 s l An ammeter is used to measure amps

Calculating Amperage If we have a 100 watt lamp plugged into a 120 volt receptacle, we can determine the rate of flow or the amperes for that circuit. Amps = 100 Watts / 120 Volts 100 / 120 =. 833 Amps

Difference b/t Volts and Amps l Example l Amps – you could say that… measure how much water comes out of a hose. l Volts measure how hard the water comes out of a hose.

Ohms Law l Current flow is strictly a result of how much voltage and resistance there is l To get more current l Increase voltage l Decrease resistance l Or both l To get less current to flow l Decrease voltage l Increase resistance l Or both

OHM’S LAW l When the voltage and resistance are equal in a circuit, ONE amp will flow l One volt will push one amp through one ohm of resistance A picture is worth a thousand words

Electrical Calculations – What is Ohm’s Law? I= 3 V 2Ω I = 1. 5 amps

Ohm’s law formulas Voltage is represented by the letter “V” l Amperage is represented by “I” l Resistance is represented by “R” l V=Ix. R

Amps Volts Watts The following relationship exists between Amps, Volts and Watts. Amperes are a measure of the rate of flow of electricity in a conductor. Volts are a measure of electrical pressure. Watts are a measure of the amount of energy or work that can be done by amperes and volts.

Formulas Watts = Volts x Amps Volts = Watts / Amps = Watts / Volts

What is Resistance? l The opposition to the flow of an electric current, producing heat. l The greater the resistance, the less current gets through. l Good conductors have low resistance. l Measured in ohms.

Resistance l Opposition to current flow (anything that slows down current) üUnit of measure is the ohm üMeasured with an ohmmeter

Factors that affect the resistance of a circuit l Type of material used l Conductor / Insulator / Semi-conductor Length of the circuit l Diameter of the circuit l Temperature l Connections l

Calculating Watts If a water heater operates at 20 amps on a 240 volt circuit, what is the wattage of the appliance? Watts = 240 Volts x 20 Amps 4800 Watts =240 V x 20 A Watts=4800

How is Electrical Power calculated? Electrical Power is the product of the current (I) and the voltage (v) The unit for electrical power is the same as that for mechanical power in the previous module – the watt (W) Example Problem: How much power is used in a circuit which is 110 volts and has a current of 1. 36 amps? P=IV Power = (1. 36 amps) (110 V) = 150 W

Here is an easier way to remember The three formulas

When you know the amperage and resistance of a circuit you can figure the voltage V Voltage = amperage times resistance

When you know the voltage and amperage of a circuit you can figure the resistance V Resistance = voltage divided by amperage

When you know the voltage and resistance of a circuit you can figure the amperage V V Amperage = voltage divided by resistance

Ohm’s Law l A cars headlight draws a current of 4. 2 A at the car battery’s voltage of 12 V. What is the resistance of the headlight? l I= 4. 2 A l V= 12 V l R=? l R= V I l R= 12 V 4. 2 A l R= 2. 85 V/A~ 2. 9Ω

Direct Current and Power l Power measures how fast work is done l Work = joules l Time= seconds l Power= J/s l Power= Watts (W)

Direct Current and Power l Power is directly related to energy l In fact when the electric company charges a home for “power” they are actually charging for energy used, not how fast you use the energy

Electrical Power and Energy l Electrical energy is measured in kilowatthours (k. Wh) l Energy= l Power x Δt Electrical Power is measured in Watts l Power l P= = voltage x current Vx. I

DC Electrical Power l A flashlight bulb draws 4. 17 A when lighted. If it has a resistance of 1. 44 Ω, what power does it draw from the 6. 00 V battery? l l l V= 6. 00 V I= 4. 17 A R= 1. 44 Ω l P= IV P= (6 V)(4. 17 A)= 25. 02 W

DC Electrical Power l The following formulas will also work: l P= I 2 R l Because P= VI and V= IR So if I replace IR for V l P= I x R x I l P= I 2 R l P= (4. 17 A)2(1. 44 Ω)= 25. 04 W l l P= V 2/R l Because P= V x I and I= V/R So if I replace V/R for I l P= V x V/R l P= V 2/R l P= (6. 0 V)2/(1. 44 Ω)= 25. 00 W l

How can we control currents? l With circuits. l Circuit: is a path for the flow of electrons. We use wires.

Direct Current l So how do we control a current l With a SWITCH- a conductor that can open and close a gap in a circuit l When the switch is open the circuit is open and electricity does not flow l When the switch is closed the circuit is closed and the electricity flows

SWITCH l. A switch is a conductor that bridges the gap in a circuit l It is like a drawbridgel When the bridge is down the people can pass- you have a closed circuit l When the bridge is up no one can pass- you have an open circuit

What is the difference between an open circuit and a closed circuit? A closed circuit is one in which the pathway of the electrical current is complete and unbroken. An open circuit is one in which the pathway of the electrical current is broken. A switch is a device in the circuit in which the circuit can be closed (turned on) or open (turned off).

Direct Current l Two types of Circuits: l Series Circuit l Parallel Circuits l. A can be controlled by a switch is a metal conductor that is able to open and close a circuit

What are electric circuits? Circuits typically contain a voltage source, a wire conductor, and one or more devices which use the electrical energy. What is a series circuit? A series circuit is one which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit will fail.

There are 2 types of circuits: l Series Circuit: the components are lined up along one path. If the circuit is broken, all components turn off.

Series Circuit

Series Circuit Rules Only one path l Amperage stays the same l Each resistance adds up to the total l l R 1 l +R 2 =Rt Voltage divided between the loads (all used up or dropped)

There are 2 types of circuits: l Parallel Circuit – there are several branching paths to the components. If the circuit is broken at any one branch, only the components on that branch will turn off.

Parallel Circuit

What is a parallel circuit? A parallel circuit has multiple pathways for the current to flow. If the circuit is broken the current may pass through other pathways and other devices will continue to work.

Electrical Safety Becoming Part of a Circuit l Short Circuit— A connection that allows a current to take an unintended path. l If you touch an exposed wire in the house, 120 Volts of current will pass into your body. This is called a SHOCK.

Household Circuits: Must be wired in Parallel l Electricity is fed into a home by Thick and Heavy wires called lines. These have low resistance. l Parallel branches extend from the lines to the wall sockets and Appliances. l Switches are placed to control branches of circuits one at a time. l Voltage in house circuits is 120 Volts. l

3. Fuses and Circuit Breakers: l When a wire carries more current than it is designed to carry it will get HOT. The insulation will then burn. l Fuse-A device with a thin strip of wire (metal) that will melt if too much current flows. This is part of the circuit. (When the fuse melts or “blows” the circuit is broken. ) l Circuit Breaker- device which uses an electromagnet to turn off a circuit when it is overloaded. l

Electric Shocks: l l l The human body depends on tiny electrical pulses to control many processes (ex. Heart beat) An electrical shock may disrupt these processes. The severity of the shock depends on the current. A current of 0. 2 amps will burn and travel across the body and could stop the heart. Current of an electric shock is related to voltage and resistance. Your body has a low resistance (ions in fluids) When wet your bodies resistance is hundreds of times lower.

That’s It !!!!