Chapter 3 - Electrical Properties
Chapter 4 - Electrical Quantities
 Making Molecules with Atoms
 http://www.youtube.com/watch?v=IOXxFaH
bIXg
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)
–How many electrons in Orbit N
14
sub-shell f?
http://en.wikipedia.org/wiki/Electron_shell
Orbit 1
Orbit 2
Orbit 3
Orbit 4
Orbit 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)
Resistive
Constants
Static Electricity
 Shielding wire
 EMI (ElectroMagnetic Interference)
 Grounding
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
 Relational Force between particles
𝑞1 𝑞2
𝐹=𝑘 2
𝐷
F = force in Newtons
q1, q2 = the charges in coulomb units
=?
= .4mC
56nC
k = Coulomb’s constant = 8.988x109
Answer
d = distance in meters between charges = 5mm
8053 N
d - Can also be imagined as the area in the electric field
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
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)