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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)