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Chapter 3 - Electrical Properties
Chapter 4 - Electrical Quantities
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.
 Each atom has a unique and specific
number of electrons surrounding the
nucleus.
 This is what makes each element different.
Electrons vs. Protons
 Electrons are negatively charged (-)
 Protons are positively charged (+)
 Electrons and protons attract each other
Electron shells

There can be as many as 7 shells / orbits
Shell Number
Number of Electrons in that shell
50
32
18
8
n =1
2
Number of electrons in each shell
Each shell is
split up into
Subshells
Shell 1
Shell 2
Shell 3
Shell 4
Shell 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.
Atoms tend to want to have
exactly 8 valence electrons
 Bonding occurs to facilitate this
 Current is possible because of this
Note: Although it looks as though there are
way more than 8 electrons in the 3rd shell,
which makes it seem that it is possible to
have more than 8 valence electrons, the order
in which the shells are filled is not sequential.
See video on next page for more info.
1
Number of Valence Electrons
2
Max
number of valence electrons is 8
Transition
metals
34 56 7
8
2 2 22222222
See this video for an explanation of why transition metals all have 2 valence electrons
https://www.youtube.com/watch?v=1TZA171yxY4&feature=youtu.be
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)
Coulomb Units
1 Coulomb is like a large group of electrons
6.24x1018 electrons =
6,240,000,000,000,000,000 electrons
1 amp = 1 Coulomb/sec
So how many Coulomb’s is 1 electron???
1.6 x 10-19 C = .00000000000000000016 C
Resistive
Constants
Random video of the day
Start at 28 min to 29min
If it doesn’t show up, search “Search for the
Super Battery” by PBS
Random Video of the Day
Lizard.wmv
B*C
F=A
D2
A=2
B=3
C=4
D=2
F =?
Coulomb’s Law of Charges
1 Coulomb is like a large group of electrons
6.25x10^18 electrons
So how many Coulomb’s is 1 electron??? 1.6 x 10-19 C
𝑞1 𝑞2
 Relational Force between particles 𝐹 = 𝑘
2
𝐷
=?
F = force in Newtons
q1, q2 = the charges in coulomb units = 0.4mC 56nC
k = Coulomb’s constant
= 8.988x109
d = distance in meters between charges = 5mm
d - Can also be imagined as the area in the electric field
Force = 8053 Newtons
How would you solve for D?
𝑞1 𝑞2
𝐹=𝑘 2
𝐷
More Coulomb’s Law practice
problems...(aka worksheet)
 Reminder of Tardys
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
Conventional Current Flow
Electron Flow
+
-
+
-
 Which one do we use???
• Electron Flow
 However I will still call it current. 
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.
6.25 x
1018
electrons
Coulomb
= 1 Amp
=1
second
second
Q
I=
t
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
The energy possessed by a
body because of its motion
ie: a roller coaster, a moving
car

Potential Energy
The energy of a particle or system of
particles derived from position, or
condition, rather than motion.
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:
• When you see it:
• Maximum spark:
2,000 V
8,000 V
25,000 V
Other Voltage Examples
 AA, AAA, C, D batteries:
 Car Battery:
 Cell Phone Battery:
 Watch Battery:
 Your Computer?:
1.5 V
12V
3.7 V – 4 V
3V
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=FGoaX
ZwFlJ4
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
1
Measured in Siemens [S]
G=
R
A practical Electric Circuit
Below is a schematic diagram of a flashlight.
Schematic Symbols (pg 59 of book)
Breadboarding Basics
What is a Breadboard?
What the purpose of a breadboard?
What circuit are we going to breadboard today?
Show large breadboard
How to use a breadboard
How does a breadboard work?
Are these wires connected?
Which is Correct???
You can also connect Integrated Circuits
(IC’s)
http://www.youtube.com/watch?v=oiqNaSPTI
7w
LAB
Intro to breadboard
Questions
 Why is the protoboard sometimes referred
to as a breadboard?
 What is the purpose of the bus strips?
 What is the purpose of the recessed center
divider?
 How would you connect 15 components
together?
 Make sure to read discussion