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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 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:**

the charge produced by the field the distance of field

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**Static Electricity DEFINITION:**

Net accumulation of electric charges on an object. 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 Contact Induction

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Friction Since opposite charges attract, the electrons move from the hair to the comb. 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. 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) 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. Ie: lightening, touching a doorknob

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Attract or Repel? Attract

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Attract or Repel? 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.**

SI unit = (Amps) A

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**2 types of current A/C – alternating current D/C – direct current**

ie: by plugging into the household wiring D/C – direct current ie: batteries

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Conductor 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.

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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. 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

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**Conductor or Insulator ?**

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**Conductor or Insulator ?**

Ceramic

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**Conductor or Insulator ?**

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**Conductor or Insulator ?**

Copper

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**Conductor or Insulator ?**

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**Conductor or Insulator ?**

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**

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**To sum them up….. silver glass copper rubber gold oil aluminum asphalt**

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

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**Mini Quiz The build up of charges on an object is called?**

Electrons do not move through… 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. SI unit = Ohm’s (W) See pg Fig. 8

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**What effects resistance?**

Temperature Thickness Length

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**Think of a common household item that has a resistor**

Something we use in class?

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**Potential Difference - Voltage**

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**

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 friction resistance (R) Ohms W

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**How do you remember the formula?**

…..if this helps, use it.

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**Practice problems resistance – R = 75 ohms voltage – V = 110 volts**

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: resistance – R = 75 ohms voltage – V = 110 volts Need to know amps 110V = I x 75 ohms (rearrange formula) Amps = 110 volts / 75 ohms (W) 1.5A

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**Practice problems resistance = 250 ohms current = 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: 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 237.5V

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**Mini Quiz ___ is a flow of electrons thru a wire or conductor. Current**

A current must have a constant flow of ___ Current Potential Difference

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**Mini Quiz Tendency for a material to oppose the flow of electrons**

What 3 quantities are related to Ohm’s Law Resistance Voltage, current, and resistance

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**Review Quiz of 20.2 before next section**

View here

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20.3 20.3 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.**

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.**

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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**Power = current x voltage**

Electrical Power Expressed in watts (W) or kilowatts (kW) 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 Circuit**

Christmas lights are an example of ….. Household wiring are wired by … Circuit Series Circuit Parallel Circuits

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**Number your paper 1-9. View here**

Video quiz Number your paper 1-9. View here

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**Check your answers 9. Swimming pool 1. c) electrons Open area**

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

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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.

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