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Pre-Test

1. Arrange proton, neutron, and electron in order of mass lowest to highest.

2. What is the charge on each?

3. Describe the behavior of like and unlike charges.

4. How do the number of electrons and protons in an atom compare?

5. What is the net charge on a normal atom?

6. What is an ion? How are they created?

7. Estimate how many electrons are in your pencil.

8. Define conductor and insulator.

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Atom Basic ReviewAtom Basic ReviewProtons and neutrons are in Protons and neutrons are in the nucleus, surrounded by the nucleus, surrounded by electrons.electrons.

++

+

–

––

+

–

atom nucleus

Proton (positive charge)

neutron (neutral)

electron (negative charge)

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Relative MassesRelative Masses

Neutron > Proton >>>>>> ElectronNeutron > Proton >>>>>> Electron

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How many electrons and How many electrons and protons are shown in the protons are shown in the atom above?atom above?

Normal neutral atoms have Normal neutral atoms have equal numbers so TOTAL equal numbers so TOTAL charge = 0charge = 0

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The Rules of Static Electricity

+ +

+

-

-The total amount of charge is conserved

Opposites attract; Likes RepelOpposites attract; Likes Repel

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Electron affinityElectron affinity

Some materials hold electrons more Some materials hold electrons more tightlytightlyHolds Electrons Strongly

Sulfur

Brass

Copper

ebonite

wax

silk

lead

fur

wool

glass

Hold Electrons Weakly

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Charging By Friction Charging By Friction

Simplest way to create a Simplest way to create a

chargecharge Tear electrons away from one object onto Tear electrons away from one object onto

anotheranother

88

99

1010

Electrons move easily in Electrons move easily in conductorsconductors but are stuck but are stuck

with their atoms in with their atoms in insulatorsinsulators..

Conductors have “sea of electrons”Conductors have “sea of electrons”

1111

Induction: A Neutral conducting Induction: A Neutral conducting object gains or loses electrons when object gains or loses electrons when a charged object is brought close to a charged object is brought close to

it.it.

1212Electric force : Attraction or repulsion Electric force : Attraction or repulsion push/pull on charged objectspush/pull on charged objects

Stronger if the charge is greaterStronger if the charge is greater

Stronger if the objects are Stronger if the objects are closercloser

1313

Graph the following force data for Graph the following force data for two charged objects separated by two charged objects separated by changing distance:changing distance:

Distance (mm) Force (N)

1 243

3 27

5 10

7 5

9 3

Use you graph to predict what the force Use you graph to predict what the force would be at 6 mm:would be at 6 mm:

1414

Electric Field: Area of lines that show the Electric Field: Area of lines that show the direction of force on any nearby positive direction of force on any nearby positive

chargescharges

1515

Electric Field: Area of lines that show the Electric Field: Area of lines that show the direction of force on any nearby positive direction of force on any nearby positive

chargeschargesDraw the electric field for a Draw the electric field for a

positive charge and a negative positive charge and a negative charge:charge:

1616

1717

1818

Light BulbLight Bulb

Electrons can Electrons can move move

through the through the bulb in bulb in either either

directiondirection

1919

To create a flow of electrons in the wires To create a flow of electrons in the wires we must have;we must have;

1.1.A source of voltage (electric pressure) A source of voltage (electric pressure) for the electronsfor the electrons

2.2.A complete conducting pathway for the A complete conducting pathway for the electrons (complete circuit)electrons (complete circuit)

2020

Potential Difference (also called Voltage) : Energy electrons lose/gain from a power supply

Current tells us how many electrons are moving between two points per unit of time

2121

Pipe = WirePipe = Wire

Water Flow = CurrentWater Flow = Current

Water = electronsWater = electrons

Water Pressure = VoltageWater Pressure = Voltage

Pump = ?Pump = ?

Water-Circuit Analogy

2222

Resistance: Opposition to the flow of Resistance: Opposition to the flow of chargescharges

Units: Ohms Units: Ohms ΩΩ

Conductors: Low ResistanceConductors: Low Resistance

Insulators: High ResistanceInsulators: High Resistance

2323

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Ohm’s Law : V = IROhm’s Law : V = IR

2525

Paul’s air conditioner runs off the 120 Volt power supply. If it draws 3 Amps of

current, what is the resistance of the air conditioner unit?

2626

If a wire has a resistance of 1.94 If a wire has a resistance of 1.94 ΩΩ and is and is connected to a 9.0 V battery, how much connected to a 9.0 V battery, how much

current will travel through the wire? current will travel through the wire?

2727

The heating element in a toaster has a resistance of 30 Ohms. If the heating

element draws 7.33 Amperes (Amps), what is the voltage across the toaster ?