Lecture 3Lecture 3

Chapter 3 - Electrical Chapter 3 - Electrical PropertiesProperties

Chapter 4 - Electrical Chapter 4 - Electrical QuantitiesQuantities

Making Molecules with Atoms http://www.youtube.com/watch?

v=qmgE0w6E6ZI ok

Elements and CompoundsElements and Compounds

Element - a substance that cannot Element - a substance that cannot be reduced to a simpler substance be reduced to a simpler substance by chemical meansby chemical means

ie: iron, gold, silver...ie: iron, gold, silver...

AtomsAtoms

The smallest particle of an element The smallest particle of an element that retains the characteristics of that retains the characteristics of that element.that element.

Atoms are like letters, molecules Atoms are like letters, molecules are like wordsare like words

ie: the water moleculeie: the water molecule

Electrons vs. ProtonsElectrons vs. Protons

Electrons are negatively charged Electrons are negatively charged (-)(-)

Protons are positively charged (+)Protons are positively charged (+) Electrons and protons attract each Electrons and protons attract each

otherother

Atomic NumberAtomic Number

Atomic Number is the number of Atomic Number is the number of protons in its nucleusprotons in its nucleus

Electron orbitsElectron orbits Electrons can only “jump” orbits or Electrons can only “jump” orbits or

shells in stepsshells in steps

The number of electrons in any particular orbit follows the equation:

# Electrons = 2n2

n = orbit number

Electron OrbitsElectron Orbits

There can be as many as 7 shells There can be as many as 7 shells in an atomin an atom

– K, L, M, N, O, P, and QK, L, M, N, O, P, and Q How many electrons, if full, would How many electrons, if full, would be in 7th shell?be in 7th shell?

How many shells would the How many shells would the electrons in the silver atom fill?electrons in the silver atom fill?

Sub-shells of OrbitsSub-shells of Orbits

–Each Orbit (K, L, M, N, O, P, Each Orbit (K, L, M, N, O, P, and Q) and Q)

has sub-shells (s, p, d, f, g)has sub-shells (s, p, d, f, g)

http://en.wikipedia.org/wiki/Electron_shell

–How many electrons in Orbit How many electrons in Orbit N N

sub-shell f?sub-shell f?1414

Orbit 1Orbit 2

Orbit 3

Orbit 4Orbit 5

.

.

.

Subshell 1

Subshell 2

Subshell 3

Subshell 4

Subshell 5

Valence ElectronsValence Electrons

The valence electron is the number The valence electron is the number of electrons in the outermost sub-of electrons in the outermost sub-shell of an atom.shell of an atom.

Valence electrons may be easy or Valence electrons may be easy or hard to be freed. Atoms tend to hard to be freed. Atoms tend to want to be neutral.want to be neutral.

How many valence electrons in silver?

1

How many valence electrons in silver?

1

How many valence electrons in gold?

1

How many valence electrons in aluminum?

3

Conductors vs. InsulatorsConductors vs. Insulators

Conductors usually have 3 or less valence electrons. Conductors usually have 3 or less valence electrons. Why?Why? Insulators usually have 5 or more valence electrons.Insulators usually have 5 or more valence electrons.

Semiconductors?Semiconductors?• How many valence electronsHow many valence electrons• DefinitionDefinition

Best Conductors:Best Conductors:• SilverSilver• CopperCopper• GoldGold• AluminumAluminum

Good InsulatorsGood Insulators• RubberRubber• PlasticPlastic• GlassGlass

Common semiconductorsCommon semiconductors• GermaniumGermanium• SiliconSilicon

ResistiveConstants

Static ElectricityStatic Electricity

Shielding wireShielding wire EMI (ElectroMagetic Interference)EMI (ElectroMagetic Interference) GroundingGrounding

IonizationIonization

Positive vs Negative ionsPositive vs Negative ions

Random Video of the DayRandom Video of the Day

Lizard.wmv

B * CB * C

RR22AA

A = 2A = 2B = 3B = 3C = 4C = 4R = 2R = 2

F =F =

F = ?F = ?

Coulomb’s Law of ChargesCoulomb’s Law of Charges

Relational Force between particlesRelational Force between particles

F = force in Newtonsq1, q2 = the charges in coulomb units

ke = constant = 8.988x109

r = distance in meters between charges

= ?= .4mC 56nC

= 5mm

1 Coulomb is like a large group of electrons6.25x10^18 electrons

r - Can also be imagined as the area in the electric field

Answer8053 N

So how many Coulomb’s is 1 electron??? 1.6 x 10-19 C

More Coulomb’s Law More Coulomb’s Law practice problems...(aka practice problems...(aka worksheet)worksheet)

Chapter 4 – Electrical Chapter 4 – Electrical PropertiesProperties

What is Current?What is Current?

What is Voltage?What is Voltage?

What is What is Resistance?Resistance?

Kinetic vs Potential EnergyKinetic vs Potential Energy

Kinetic EnergyKinetic Energy Potential EnergyPotential EnergyThe energy possessed by a body because of its motion

The energy of a particle or system of particles derived from position, or condition, rather than motion.

ie: a roller coaster, a moving car ie: a stretched rubber band, a coiled

spring.

In our case, a BATTERY!

Introduction VideoIntroduction Video

http://www.youtube.com/watch?v=EJeAuQ7pkpc&feature=fvw

CurrentCurrent

Current is a movement of charged Current is a movement of charged particlesparticles

Within metal conductors, the charged Within metal conductors, the charged particles that are moving are particles that are moving are electrons.electrons.

These electrons flow when there is a These electrons flow when there is a potential difference in the charges potential difference in the charges across a conductor. Aka: protons are across a conductor. Aka: protons are on the other side. on the other side.

Current – electron flow Current – electron flow modelmodel The current you are used to working with is The current you are used to working with is

nothing more than moving electrons, moving nothing more than moving electrons, moving from a region of negative charge to an area of from a region of negative charge to an area of positive charge.positive charge.

As a potential difference is impressed across the As a potential difference is impressed across the conductor, the positive terminal of the battery conductor, the positive terminal of the battery attracts electrons beyond point A. Point A attracts electrons beyond point A. Point A becomes positive because it now has an electron becomes positive because it now has an electron deficiency. As a result, electrons are attracted deficiency. As a result, electrons are attracted from point B … and so on. from point B … and so on.

This is true for metal conductors.This is true for metal conductors.

Current – Conventional Current – Conventional current flowcurrent flow

If you Google “current” or look in a If you Google “current” or look in a friends electrical engineering book, you friends electrical engineering book, you might find that current flows from might find that current flows from positive to negative.positive to negative.

A few perspectives on this include:A few perspectives on this include:• Currents of positive ionsCurrents of positive ions• Hole Charge Current in p-type semiconductorsHole Charge Current in p-type semiconductors

Arrows shown on diodes and transistors Arrows shown on diodes and transistors are for current, not electron floware for current, not electron flow

Electron Flow vs. Conventional Electron Flow vs. Conventional Current FlowCurrent Flow

Which one do we use???Which one do we use???• Electron FlowElectron Flow

However I will still call it current. However I will still call it current.

+-

+-

Electron FlowConventional Current Flow

Current MagnitudeCurrent Magnitude If the potential difference is increased, If the potential difference is increased,

the electric field is stronger, the the electric field is stronger, the amount of energy imparted to a amount of energy imparted to a valence electron is greater, and the valence electron is greater, and the magnitude of current is increased.magnitude of current is increased.

Current MagnitudeCurrent Magnitude If 6.25 x 10If 6.25 x 101818 electrons pass a electrons pass a

given point in one second, then given point in one second, then this is called one amp.this is called one amp.

electrons second

6.25 x 1018 Coulomb second

= 1 = 1 Amp

Q t

I =

VoltageVoltage

So what causes there to be a So what causes there to be a potential difference in charges potential difference in charges across a conductor?across a conductor?• (how do you get protons to be stored on (how do you get protons to be stored on

one side and electrons on the other?)one side and electrons on the other?) There are 6 ways this can be done, There are 6 ways this can be done,

and this is part of your homework to and this is part of your homework to look up.look up.

VoltageVoltage

Voltage is also known asVoltage is also known as• Electromotive Force (EMF)Electromotive Force (EMF)

– Usually associated with the voltage a Usually associated with the voltage a battery makesbattery makes

• Potential differencePotential difference– Difference in chargesDifference in charges

Voltage ExampleVoltage Example

How much voltage is produced How much voltage is produced when you shock someone?when you shock someone?• When you feel it:When you feel it: 2,000 V2,000 V• When you see it:When you see it: 8,000 V8,000 V• Maximum spark:Maximum spark: 25,000 V25,000 V

Other Voltage ExamplesOther Voltage Examples

AA, AAA, C, D batteries:AA, AAA, C, D batteries: 1.5 V1.5 V Car Battery:Car Battery: 12V12V Cell Phone Battery:Cell Phone Battery: 3.7 V – 3.7 V –

4 V4 V Watch Battery:Watch Battery: 3V3V Your Computer?:Your Computer?: 5V5V

Voltage in a batteryVoltage in a battery

Just like a rubber band that has Just like a rubber band that has been stretched, there is potential been stretched, there is potential for it to do work when released.for it to do work when released.

This is similar to the storage of This is similar to the storage of voltage in a batteryvoltage in a battery

Batteries only have a certain Batteries only have a certain amount of charge stored before amount of charge stored before they run out.they run out.

Voltage is RelativeVoltage is Relative

Clapping exampleClapping example Without a reference point, a voltage Without a reference point, a voltage

of 12V is meaningless.of 12V is meaningless. The reference point for voltage The reference point for voltage

most of the time is ground, or 0V.most of the time is ground, or 0V. However, there are different types However, there are different types

of grounds. How is an airplane of grounds. How is an airplane grounded?grounded?

Voltage is Relative (cont.)Voltage is Relative (cont.)

For example, what is the For example, what is the voltage at this point, if each voltage at this point, if each battery is 1.5V?battery is 1.5V?

Depends, if its referenced to:Depends, if its referenced to:• GroundGround• Negative side of same batteryNegative side of same battery• Top of battery above…Top of battery above…

+

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ResistanceResistance

Resistance is an opposition to current flowResistance is an opposition to current flow Resistance can be made by:Resistance can be made by:

• Varying the type of material, (think valence Varying the type of material, (think valence electrons)electrons)

• Varying the length of materialVarying the length of material• Varying the amount or cross-section of materialVarying the amount or cross-section of material

Resistors are like poor conductors. The are Resistors are like poor conductors. The are somewhere between a conductor and an somewhere between a conductor and an insulatorinsulator

Resistors (cont.)Resistors (cont.)

Resistors are a little like transducers in that they convert electrical energy into heat.

Voltage is converted into heat when electrons bump into each other so voltage is lost.

What is the opposite of What is the opposite of resistance?resistance?

ConductanceConductance

G = 1R

Measured in Siemens [S]

Voltage, current & Voltage, current & resistance analogyresistance analogy

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A practical Electric CircuitA practical Electric Circuit

Below is a schematic diagram of a flashlight.

Schematic Symbols (pg 59 of book)Schematic Symbols (pg 59 of book)

LABLAB