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Electricity

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20.1 Electric Charge & Static Electricity

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Force Electric forces – attractive or repulsive Electric forces – attractive or repulsive What does this mean? What does this mean?

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Opposites attract

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Like charges repel

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And remember….

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Electric Fields Strength of a field depends on: Strength of a field depends on: the charge produced by the field the charge produced by the field the distance of field the distance of field

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Static Electricity DEFINITION: DEFINITION: Net accumulation of electric charges on an object. IN OTHER WORDS: IN OTHER WORDS: Electrons that are moved from 1 place to another usually by rubbing, brushing or no contact.

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Static charges work 3 ways Friction Friction Contact Contact Induction Induction

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Friction Since opposite charges attract, the electrons move from the hair to the comb. Since opposite charges attract, the electrons move from the hair to the comb. The comb is now negatively charged by FRICTION. The comb is now negatively charged by FRICTION.

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For the visual learners...

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Contact Van deGraaff generator has a – charge at top. Touching top would make the object – charged. Van deGraaff generator has a – charge at top. Touching top would make the object – charged. The object is now negatively charged by CONTACT. The object is now negatively charged by CONTACT.

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Induction - charges in hand cause the + charges in the doorknob to move to the opposite side (opposites attract) - charges in hand cause the + charges in the doorknob to move to the opposite side (opposites attract) Charge has been transferred by INDUCTION. Charge has been transferred by INDUCTION.

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For the visual learners….

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Static Discharge When a pathway that charges can move through forms suddenly. When a pathway that charges can move through forms suddenly. Ie: lightening, touching a doorknob Ie: lightening, touching a doorknob

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Attract or Repel? Attract

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Repel

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What’s the best thing about static electricity?

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Lecture 20.2 You need a calculator

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20.2 Electric Current & Ohms’s Law

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Current The flow of electrons through a wire or a conductor. The flow of electrons through a wire or a conductor. SI unit = (Amps) A SI unit = (Amps) A

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2 types of current A/C – alternating current A/C – alternating current ie: by plugging into the ie: by plugging into the household wiring household wiring D/C – direct current D/C – direct current ie: batteries ie: batteries

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Conductor DEFINITION: Material that allows electrons to move easily through it. DEFINITION: Material that allows electrons to move easily through it. IN OTHER WORDS: Just like a train conductor moves cars from one track to another track, conductors move electrons from one place to another. IN OTHER WORDS: Just like a train conductor moves cars from one track to another track, conductors move electrons from one place to another.

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Which metal is the best conductor for your internet connection?

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Copper? Silver?

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Insulator DEFINITION: Material that does not allow electrons to move through it. DEFINITION: Material that does not allow electrons to move through it. IN OTHER WORDS: Just as a potholder insulates you from heat, electrical insulators slow down or resist the flow of electricity. IN OTHER WORDS: Just as a potholder insulates you from heat, electrical insulators slow down or resist the flow of electricity.

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Conductor or Insulator ? Glass Glass

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Conductor or Insulator ?

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Ceramic Ceramic

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Conductor or Insulator ?

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Copper Copper

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Conductor or Insulator ?

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Wood Wood

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Conductor or Insulator ? Although uncommon, there are a number of insulator styles made from wood. One type was made from the dense wood lignum vitae for the San Francisco trolley system.

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Everyday examples of conductors and Insulators Conductors Insulators

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To sum them up….. Conductors: silver silver copper copper gold gold aluminum aluminum iron iron steel steel brass brass bronze bronze mercury mercury graphite graphite dirty water dirty water concrete concrete Insulators: glass glass rubber rubber oil oil asphalt asphalt fiberglass fiberglass porcelain porcelain ceramic ceramic quartz quartz (dry) cotton (dry) cotton (dry) paper (dry) paper (dry) wood (dry) wood plastic plastic air air pure water pure water

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Mini Quiz 1. The build up of charges on an object is called? 2. Electrons do not move through… 3. Electrons move easily through materials called … Static Electricity Insulators Conductors

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Resistance DEFINITION: the tendency for a material to oppose the flow of electrons, changing energy into thermal energy and light. DEFINITION: the tendency for a material to oppose the flow of electrons, changing energy into thermal energy and light. SI unit = Ohm’s ( SI unit = Ohm’s ( See pg. 605 Fig. 8 See pg. 605 Fig. 8

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What effects resistance? Temperature Thickness Length

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Something we use in class? Think of a common household item that has a resistor

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Potential Difference - Voltage DEFINTION: Difference in potential between 2 different places. DEFINTION: Difference in potential between 2 different places. IN OTHER WORDS: It is the amount of work that must be done to carry a charge from one point to another.

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A source of potential difference must keep the current flowing.

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Ohm’s Law Potential difference = current x resistance Potential difference = current x resistance V (volts) = I (amperes) x R (ohms) V (volts) = I (amperes) x R (ohms) Compare to: Water in a Hose Electricity is: DC in a Wire Electrical Units Symbol pressure potential (V)Volts V rate of flow current (I) Amps (or Amperes) A frictionresistance (R) Ohms

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How do you remember the formula? …..if this helps, use it.

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Practice problems A 75 ohm circuit is powered by a 110-Volt energy source. What is the current flowing in this circuit? A 75 ohm circuit is powered by a 110-Volt energy source. What is the current flowing in this circuit? First we identify the information that we are given in the problem: First we identify the information that we are given in the problem: resistance – R = 75 ohms voltage – V = 110 volts Need to know amps 110V = I x 75 ohms (rearrange formula) Amps = 110 volts / 75 ohms (

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Practice problems What is the voltage of a circuit with a resistance of 250 ohms and a current of 0.95 amps? What is the voltage of a circuit with a resistance of 250 ohms and a current of 0.95 amps? First we identify the information that we are given in the problem: First we identify the information that we are given in the problem: resistance = 250 ohms current = 0.95 amps Need to know volts V= 250 ohms x 0.95 amps Volts = 250 ohms x 0.95 amps V

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Mini Quiz ___ is a flow of electrons thru a wire or conductor. ___ is a flow of electrons thru a wire or conductor. A current must have a constant flow of ___ A current must have a constant flow of ___ Current Current Potential Difference Potential Difference

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Mini Quiz Tendency for a material to oppose the flow of electrons Tendency for a material to oppose the flow of electrons What 3 quantities are related to Ohm’s Law What 3 quantities are related to Ohm’s Law Resistance Resistance Voltage, current, and resistance Voltage, current, and resistance

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Review Quiz of 20.2 before next section View here View here

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Electric Circuits

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Circuit is a closed path through which electrons can flow.

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Circuit Symbols

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Series Circuit Christmas lights are often wired this way. Christmas lights are often wired this way. Disadvantage – when 1 light goes out the whole strand goes out. Disadvantage – when 1 light goes out the whole strand goes out.

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Series Circuit

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Parallel Circuit Electricity has several paths that it can travel. Electricity has several paths that it can travel. Used in households. When one circuit is closed others still work. Used in households. When one circuit is closed others still work.

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Parallel Circuit

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Series or Parallel? Parallel

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Series or Parallel? Series

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Electrical Power Expressed in watts (W) or kilowatts (kW) Expressed in watts (W) or kilowatts (kW) The amount of power an appliance used can be calculated by The amount of power an appliance used can be calculated by Power = current x voltage Watts = amps x volts P = I x V

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Power is expressed here as E for “energy”

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Mini Quiz A _____ is a closed path in which electrons flow A _____ is a closed path in which electrons flow Christmas lights are an example of ….. Christmas lights are an example of ….. Household wiring are wired by … Household wiring are wired by … Series Circuit Series Circuit Parallel Circuits Parallel Circuits Circuit Circuit

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Video quiz Number your paper 1-9. View here View here

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Check your answers 1. c) electrons 2. a) nucleus 3. b) insulators 4. c) electrical 5. b) attract 6. c) positive 7. b) neutral 8. d) negative 9. Swimming pool Swimming pool Open area Open area Climbing on a metal ladder Climbing on a metal ladder Fishing in a metal boat on a lake Fishing in a metal boat on a lake Standing in a field wearing a metal suit Standing in a field wearing a metal suit

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The End

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Electroscope An instrument for detecting the presence of static electricity. When the leaves are charged the same way they repel each other. When the leaves are charged the same way they repel each other.

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