Chapter 3 - Electrical Properties Chapter 4 - Electrical Quantities

Chapter 3 - Electrical PropertiesChapter 4 - Electrical Quantities

Making Molecules with Atoms http://

www.youtube.com/watch?v=IOXxFaHbIXg

Elements and Compounds

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

ie: iron, gold, silver...

Atoms

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

Atoms are like letters, molecules are like words

ie: the water molecule

Electrons vs. Protons

Electrons are negatively charged (-)

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

other

Atomic Number

Atomic Number is the number of protons in its nucleus

Electron orbits Electrons can only “jump” orbits or

shells in steps

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

# Electrons = 2n2

n = orbit number

Electron Orbits

There can be as many as 7 shells in an atom

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

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

Sub-shells of Orbits

–Each Orbit (K, L, M, N, O, P, and Q)

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

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

–How many electrons in Orbit N

sub-shell f?14

Orbit 1Orbit 2

Orbit 3

Orbit 4Orbit 5

.

.

.

Subshell 1

Subshell 2

Subshell 3

Subshell 4

Subshell 5

Valence Electrons

The valence electron is the number of electrons in the outermost shell of an atom. (Not sub-shell) http://au.answers.yahoo.com/question/index?qid=20080327135829AA6jdpj Valence electrons may be easy or hard to be freed. Atoms tend to want to be neutral.

How many valence electrons in copper?

1

Conductors vs. Insulators

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

Semiconductors?• How many valence electrons• Definition

Best Conductors:• Silver• Copper• Gold• Aluminum

Good Insulators• Rubber• Plastic• Glass

Common semiconductors• Germanium• Silicon

Semiconductors

Conductivity increases with increasing temperature• This is opposite of metal

Useful properties• Can pass current more easily in one direction than

the other, • Variable resistance• Sensitivity to light or heat.

Conductivity can be modified by adding impure atoms (atoms that are not purely semiconductive)

ResistiveConstants

Static Electricity

Shielding wire EMI (ElectroMagnetic Interference) Grounding

Random Video of the Day

Lizard.wmv

B * C

D2A

A = 2B = 3C = 4D = 2

F =

F = ?

Coulomb’s Law of Charges

Relational Force between particles

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

k = Coulomb’s constant = 8.988x109

d = distance in meters between charges

= ?= .4mC 56nC

= 5mm

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

d - 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

𝐹=𝑘𝑞1𝑞2

𝐷2

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

Chapter 4 – Electrical Properties

What is Current?

What is Voltage?

What is Resistance?

Voltage, current & resistance analogy

- ------ --- -

-

Introduction Video

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

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

Current

Current is a movement of charged particles

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

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

Current – electron flow model The current you are used to working

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

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

This is true for metal conductors.

Current – Conventional current flow If you Google “current” or look in a

friends electrical engineering book, you might find that current flows from positive to negative.

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

semiconductors Arrows shown on diodes and transistors

are for current, not electron flow

Electron Flow vs. Conventional Current Flow

Which one do we use???• Electron Flow

However I will still call it current.

+-

+-

Electron FlowConventional Current Flow

Current Magnitude If the potential difference is

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

Current Magnitude If 6.25 x 1018 electrons pass a

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

electrons second

6.25 x 1018 Coulomb second

= 1 = 1 Amp

Q t

I =

Voltage

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

on one side and electrons on the other?)

There are 6 ways this can be done, and this is part of your homework to look up.

Kinetic vs Potential Energy

Kinetic Energy Potential 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!

Voltage

Voltage is also known as• Electromotive Force (EMF)

– Usually associated with the voltage a battery makes

• Potential difference– Difference in charges

Voltage Example

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

Other Voltage Examples

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

4 V Watch Battery: 3V Your Computer?: 5V

Voltage in a battery

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

This is similar to the storage of voltage in a battery

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

Voltage is Relative

Clapping example Without a reference point, a

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

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

of grounds. How is an airplane grounded?

Voltage is Relative (cont.)

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

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

+

-

Another RVOTD

https://www.youtube.com/watch?v=FGoaXZwFlJ4

Resistance

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

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

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

material Resistors are like poor conductors. The

are somewhere between a conductor and an insulator

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 resistance?

Conductance

G = 1R

Measured in Siemens [S]

A practical Electric Circuit

Below is a schematic diagram of a flashlight.

Schematic Symbols (pg 59 of book)