chapter 3 - electrical properties chapter 4 - electrical quantities
TRANSCRIPT
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Chapter 3 - Electrical PropertiesChapter 4 - Electrical Quantities
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Making Molecules with Atoms http://
www.youtube.com/watch?v=IOXxFaHbIXg
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Elements and Compounds
Element - a substance that cannot be reduced to a simpler substance by chemical means
ie: iron, gold, silver...
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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
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Electrons vs. Protons
Electrons are negatively charged (-)
Protons are positively charged (+) Electrons and protons attract each
other
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Atomic Number
Atomic Number is the number of protons in its nucleus
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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
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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?
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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
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Orbit 1Orbit 2
Orbit 3
Orbit 4Orbit 5
.
.
.
Subshell 1
Subshell 2
Subshell 3
Subshell 4
Subshell 5
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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.
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How many valence electrons in copper?
1
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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
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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)
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ResistiveConstants
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Static Electricity
Shielding wire EMI (ElectroMagnetic Interference) Grounding
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Random Video of the Day
Lizard.wmv
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B * C
D2A
A = 2B = 3C = 4D = 2
F =
F = ?
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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
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More Coulomb’s Law practice problems...(aka worksheet)
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Chapter 4 – Electrical Properties
What is Current?
What is Voltage?
What is Resistance?
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Voltage, current & resistance analogy
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Introduction Video
http://www.youtube.com/watch?v=EJeAuQ7pkpc&feature=fvw
http://www.youtube.com/watch?v=EJeAuQ7pkpc&feature=fvw
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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.
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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.
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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
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Electron Flow vs. Conventional Current Flow
Which one do we use???• Electron Flow
However I will still call it current.
+-
+-
Electron FlowConventional Current Flow
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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.
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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 =
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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.
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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!
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Voltage
Voltage is also known as• Electromotive Force (EMF)
– Usually associated with the voltage a battery makes
• Potential difference– Difference in charges
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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
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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
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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.
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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?
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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…
+
-
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Another RVOTD
https://www.youtube.com/watch?v=FGoaXZwFlJ4
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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
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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.
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What is the opposite of resistance?
Conductance
G = 1R
Measured in Siemens [S]
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A practical Electric Circuit
Below is a schematic diagram of a flashlight.
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Schematic Symbols (pg 59 of book)