Electricity A source of energy that can be easily converted into light, heat, or power.

Atoms and Electricity  All matter is made of atoms  An atom is the smallest particle of any element that still retains the characteristics of that element.  An atom has a nucleus, or center, which is surrounded by an electron cloud.  The nucleus contains protons and neutrons  The electron cloud contains 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 it is called an Electrical Current - the flow of electrons!

Charge and Force Protons h h h have a positive charge (+) Neutrons have no charge Electrons have a negative charge (-) An atom in its normal state has the same number or electrons as protons so it is neutrally charged. When an atom loses one or more electrons (Positive Ion), it has a positive net charge. When an atom gains one or more electrons (Negative Ion), it has a negative net charge. AA f ff force is a p pp pull or push on an object

Static Electricity Static electricity is the build up of electric charges that stays on an object. Static electricity is the build up of electric charges that stays on an object. Charges do not flow they remain at rest. Charges do not flow they remain at rest. Electric Discharge - the loss of Static electricity as electric charges move off an object. Electric Discharge - the loss of Static electricity as electric charges move off an object. Lightning Lightning

What is static electricity? When two objects rub against each other electrons transfer and build up on an object causing it to have a different charge from its surroundings. Like the shoes rubbing against the carpet. Electrons are transferred from the carpet to the shoes.

WWWWhen charged particles come near one another, they give rise to two different forces FFFForces of attraction UUUUnlike charges attract one another ---- and + FFFForces of repulsion LLLLike charges repel one another ++++ and + or - and – TTTThe most important difference between gravitational and electrical forces is that electrical forces may be either attractive or repulsive, whereas gravitational forces are only attractive. A charge is a measure of the extra positive or negative particles that an object has.

As electrons collect on an object, it becomes negatively charged. As electrons leave an object it attains a positive charges. Charges interact with each other: Often when you remove clothes from the clothes dryer, they seem to stick together. This is because some of the clothes have gained electrons by rubbing against other clothes. The clothes losing electrons become positive. The negative clothes are attracted to the positive clothes.

What causes you to be shocked when you rub your feet across carpet? An electrical discharge is the passing of an electric current through the air from a negatively charged object to a positively charge object. This is what causes lightning !

Methods of Charging Friction – r rubbing two objects together Conduction – direct contact of objects in which electrons flow through one object to another object –(conductors) Induction – involves a rearrangement of electric charges in which a neutral object need only come close to a charged object, no contact is necessary

Law of Conservation of Charge  When we charge something, no electrons are created or destroyed.  They are simply transferred from one material to another  Charge is conserved

Coulomb’s Law and Charge Polarization The Force Between The Two Charged Particles Varies Directly As The Product Of Their Charges And Inversely As The Square Of The Separation Distance The Force Between The Two Charged Particles Varies Directly As The Product Of Their Charges And Inversely As The Square Of The Separation Distance Coulomb (C) – is the unit of charge Coulomb (C) – is the unit of charge A charge of 1 C is the charge on 6.25 billion billion electrons (6,250,000,000,000,000,000) A charge of 1 C is the charge on 6.25 billion billion electrons (6,250,000,000,000,000,000) the amount of charge that passes through a common 100-watt light bulb in little more than a second the amount of charge that passes through a common 100-watt light bulb in little more than a second  A polarized object has no net charge. Only the distribution of charge in the material is altered. (example – balloon sticking to wall - p.174)

Electrical Terms EEEElectrical Circuit – a path along which electrons can flow EEEElectric Current - the flow of electrons TTTTwo types of Electric Current: DDDDirect Current (DC) – electrons flow in one direction only (the electrons flow from the negative terminal of a battery to the positive terminal) Battery – electrons flow from repelling negative terminal toward the attracting positive terminal AAAAlternating Current (AC) – electrons in the circuit flow initially in one direction and then reverses and flows in the opposite direction (1 cycle) Generator HHHHertz – represents one cycle per second IIIIn US electrical energy is delivered at 60 Hertz (Hz) – 60 cycles per second (changes direction of flow 120 times every second)

Electrical Terms (cont.) AAAAmpere (A) or (I) – measures the rate of electrical flow AAAAn ampere is the rate of flow of 1 coulomb of charge per second (In a wire that carries 5 amperes, 5 coulombs of charge pass any cross section in the wire each second) VVVVoltage (V) or (E) – measures the electrical pressure EEEElectrons flow in a wire only when a difference in electrical pressure exists across the ends of the wire. AAAA steady current needs an “electrical pump” (batteries, generators) to provide a difference in voltage VVVVoltage produces current (if there is a complete circuit) VVVVoltage is the pressure – Current is the result

Electrical Terms (cont) OOOOhms (Ω) or (R) – measures the electrical resistance to current flow RRRResistance in a Circuit depends on: WWWWidth – narrow conductors resist electrical current more than wider conductors LLLLength long conductors offer more resistance than short conductors TTTTemperature – the higher the temp. the greater resistance a conductor has KKKKind of Material – elements that have a higher number of valence electrons have greater resistance than elements with a lower number of valence electrons. CCCConductor – material that provides a path for electrons to move Good Conductors – Silver, Copper, Gold, Platinum, Aluminum Poor Conductors (Insulators) – Rubber, Plastic, Wood, Glass Semi Conductors – neither good for conductors or insulators – elements with 4 valence electrons – silicon, germanium

OHMS LAW NNNNamed after Georg Simon Ohm –discovered a simple relationship among voltage, current, and resistance TTTThe amount of current in a circuit is directly proportional to the voltage across the circuit and inversely proportional to the resistance of the circuit So for a given circuit of constant resistance, current and voltage are proportional to each other (the greater the voltage, the greater the current) But if the resistance is doubled for a circuit, the current is reduced to half (the higher the resistance, the lower the current)

CCCCurrent = Voltage / Resistance AAAAmperes = Volts / Ohms I = E / R VVVVolts = Amps x Ohms E = I x R IIIIt takes one volt to push one amp through one ohm OOOOhms = Volts / Amps R = E / I

E = I x R I = E / R R = E / I

Electrical Power Power is the rate at which work is done or energy is used. Electrical power is a measure of the rate at which electricity does work or provides energy that is converted to another form of energy Unit of electrical power is the Watt, symbol is W or P Electrical Power = Voltage x Current Watts = Volts x Amperes W = E x I One horsepower (hp) is equal to 746 Watts W EIx

Electrical Energy Electrical energy is a measure of the amount of power used and the time of use. Electrical energy is the product of the power and the time. The unit of measure of electrical energy or work is the watthour (Wh) Kilowatt-hour (kWh) = Kilowatts x hours of use 1 kWh = 1000 W per hour Electrical energy may be transformed to : Mechanical energy – motor Light energy – lamp Thermal energy – heater W EIx

Problems VVVVolts = 12 Amps = ? Ohms = 6 Watts = ? Amps = (E/R) or (12/6) 2 Watts = (ExI) or (12x2) 24 VVVVolts = 6 Amps = ? Ohms = ? Watts = 30 Amps = (W/E) or (30/6) 5 Ohms = (E/I) or (6/5) 6/5 VVVVolts = ? Amps = 2 Ohms = 14 Watts = ? Volts = (IxR) or (2x14) 28 Watts = (ExI) or (28x2) 56 VVVVolts = ? Amps = ? Ohms = 9 Watts = 144 Watts = ExI and Volts = IxR so Watts = Ix (IxR) so 144 W = IxIx9 or I2 x9 so I2 = 144/9 or 16 so I=square root of 16 or 4 A so Volts = (IxR) or (4x9) 36 V

Example problem: Electrical Energy is measured in Kilowatt-hours so we need to determine the amount of Electrical Power first which is measured in Watts Watts = Volts x Amps Electrical Power = (120 V) (2A) = 240 W Next we will determine the Electrical energy which is measured in Kilowatt-hours kWh = (W x hrs.) / 1000 Electrical Energy = (240 W) (4 h) = 960Wh / 1000 = 0.96 kWh