Charge & Electricity Unit 6 – Lecture 1

Review 3 types of subatomic particles protons: + charged neutrons: non-charged electrons: - charge Equal p+ & e- = neutral atom or compound Objects with no net charge are called neutral

Charge Charge – a point source of electrical force two types – positive and negative opposite charges attract like charges repel most objects are neutral

Conservation of Charge Law of Conservation of Charge charges are neither created nor destroyed, they can only be transferred from one object to another

Review “Sea of Electrons” – elements in a metallic bond do not hold their electrons tightly, but share them between all atoms

Static Charge static electricity – the accumu- lation of excess electric [negative] charge on an object static = not in physical motion “static cling” – objects that are oppositely charged “stick” together

Static Charge static electricity – the accumulation of excess electric [negative] charge on an object electrons are being transferred from the carpet to your shoe electrical discharge – sudden and momentary electric current between two objects

Static Charge Lightening is a form of static discharge static charges are formed when the particles inside the storm cloud rub against each other [because of convection], separating charges.

Electric Field area around a charged object which exerts forces on other electric charges

Review Conductor a material through which electrons can move easily best are metals [sea of electrons]

Review Insulator a material through which electrons are not able to move easily plastic, wood, rubber, glass…etc

Charging Objects Charge by Contact transfer of charge by direct touch or rubbing static cling

Charging Objects Charge by Induction rearrangement of electrons in a neutral object because of a charge from a nearby object

Electricity Electric Current [I]– the net movement of electric charges in a single direction ex: spark between you and doorknob measured in Amperes [A] 1 A = 6,250 million billion electrons per second passing a single point

Electricity Volt (V) – unit of the PE of an electrical charge electricity flows from that of higher voltage to lower voltage

Resistance Resistance [R] – a material’s opposition to the flow of current measured in Ohms (Ω) resistance will turn electrical E into thermal E and light

Resistance Resistance [R] – a material’s opposition to the flow of current conductor – less resistance insulator – more resistance

Resistance Increase resistance with… increase temperature increase length decrease thickness

Resistance Decrease resistance with… more, smaller batteries shorter, thicker wire more conductive metal

V I R Electricity Ohm’s Law: Current = Voltage / Resistance I = V / R Voltage = Current * Resistance V = I * R Resistance = Voltage / Current R = V / I V I R

P V I Electricity Power (W) is measured in Watts Power = Voltage * Current Watts = Volts * Amps P = V * I P V I

Practice The current in a clothes dryer is 15 A when plugged into a 240 V outlet. How much electrical power does the clothes dryer use? 3,600 watts OR 3.6 kilowatts Calculate the voltage difference in a circuit with a resistance of 50 Ω if the current of the circuit is 0.7 A. 35 volts

Electricity Electrical Energy is measured in kilowatt hours [kWh] Electrical Energy = Electric Power * time E = P * t A microwave oven with a power rating of 1,200 W is being used for 0.25 h. How much electri- cal energy is being used by the microwave? 0.30 kWh E P t

Homework For ALL problems, show ALL work: 1. Write Equation 2. Plug In Numbers 3. THEN Solve for Answer ALL PROBLEMS MUST HAVE THESE THREE STEPS

Homework p 199 #s 6-7 p 212 #s 1-4 p 205 #s 6-7 p 213 #s 6-8