Transcript Electricity

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ELECTRICITY
Kyle Thornton
Why Study Electricity?
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Electric energy is
supplied to the x-ray
tube in order for it to
function
The x-ray tube converts
electric energy into xrays
This is the primary
function of the x-ray
unit
Electrical charge
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Electron - smallest unit of
electric charge
 A mobile charge carrier
 Can move from one point
to another
 Carries a negative
charge
Proton - Equal in mass and
weight to electron
 Bound in the nucleus
 Carries a positive charge
Terminology
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Neutral
 object has equal number of protons and electrons
Ion pair
 Electron removed from atom
Atom becomes a positive ion
 More positive charges
 Positive atom + free electron = ion pair
 Radiation passing through matter causes ion pairs potentially harmful
Ground
 A conduit for excess electric charges to move through
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Divisions Of Matter
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Insulator
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Conductor
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Does not allow an electrical charge to move freely
Allows a charge to move freely
Either through it or on its surface
Semiconductor
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A charge moves through easier than an insulator
but not as easy as a conductor
Electrostatics And
Electrification
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Electrostatics
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Non-moving electrical charges
Static electricity
Electrification
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Removal or addition of electrons
An excess or deficiency of electrons will
determine if positive or negative
Methods Of Electrification
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Friction
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Removal of electrons from one object to another
Usually by rubbing the objects together
Simplest form of electrification
Contact
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A body charged by friction touches another object
Confers the same type of charge
More Methods Of
Electrification
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Induction
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All charged objects have an electric field
Uncharged metallic object will experience an
electron shift if brought into an electric field
Only the electrons move
Laws Of Electrostatics
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1. Like charges repel; opposites attract
2. Electrostatic force - Coulomb’s law
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Inversely proportional to square of the distance between
two charged objects
3. Electric charges reside only on the surface of
conductors
4. Concentration of charges on curved surface is
greater where curvature is greatest
5. Only negative charges can move in solid
conductors
Electrodynamics
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Charges in motion
Current - Flow of charged particles
1. In a vacuum
2. In a gas
3. In an ionic solution
4. In a metallic conductor
Current is measured in amperes - A
Sources of Current
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Cells or batteries
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Dynamo or generator
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Converts chemical to
electrical energy
Mechanical to electrical
energy
Solar
Atomic
Wind
Geothermal
How does electric current flow?
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There must be a path
on which to flow
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Circuit
Generally controlled by
switches that open or
close the circuit
There must be a
potential difference
between two points
within the path
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Voltage or V
This is usually supplied
by a battery, power
supply, or electrical outlet
Resistance
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Acts to oppose current flow
Resistance is generally present in all
materials
Resistance is measured in Ohm’s or Ω
Resistance is determined by:
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The material of the conductor
The length of the conductor
The cross-section of the conductor
More on Resistance
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http://micro.magnet.fsu.edu/electromag/electr
icity/resistance.html#CODE
Ohm’s Law
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The relationship of current, voltage, and resistance
in a circuit
If voltage is increased, and electrons are available,
the electrons will move faster
Current flow is affected by resistance
Resisitors may be added to the circuit to regulate
and direct the current flowing through the circuit
file:///C:/DOCUME~1/kthornto/LOCALS~1/Temp/phe
t-ohms-law/ohms-law_en.html
Ohm’s Law, Continued
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Voltage = Current X
Resistance
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or
V=IXR
or
R = V/I
or
I = V/R
Work The Following Problem
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A 1.5 battery produces 300 mA. Determine
the resistance of the circuit.
Given:
V = 1.5
I = 300 mA = 0.3 A
R=?
Ohm’s law = V = IR or R = V/I
Answer: 1.5/0.3 = 5 ohms
Types Of Circuits
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Series
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All resistors are
connected in a
continuous line
If a resistor is damaged
so that current cannot
flow, it won’t flow through
the entire circuit
Types of Circuits
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Parallel
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All resistors are
connected side by side
If one resistor is broken,
there is still a path on
which to flow
Ohm’s Law In A Series Circuit
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Rule #1
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Rule #2
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I(T) = I(1) = I(2) = I(3)
The current in each circuit
component is constant
V(T) = V(1) + V(2) + V(3)
The total voltage is equal to
the sum of the voltage in each
component
Rule #3
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R(T) = R(1) + R(2) + R(3)
The total resistance is equal to
the sum of the resistance in
each component
Ohm’s Law Website
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http://micro.magnet.fsu.edu/electromag/java/
ohmslaw/index.html
More Practice With Ohm’s Law
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There are three resistors in a circuit. They
have the following magnitudes
R(1) = 8, R(2) = 10, R(3) = 6
What is the total resistance?
Answer = 8 + 10 + 6 = 24
Voltage = 12
Find the total current.
Current = V/R
Answer = Amperes = 12/24 = 0.5 A
Ohm’s Law In A Parallel Circuit
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Rule #1
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Rule #2
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V(T) = V(1) = V(2) = V(3)
I(T) = I(1) + I(2) + I(3)
Rule #3
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1/R(T) = 1/R(1) + 1/R(2)
+ 1/R(3)
The total resistance is
inversely proportional to
the sum of the
reciprocals of each
individual resistor
Total Resistance In A Parallel
Circuit
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R(T) will always be less than the lowest
individual resistance in the circuit
Find the total resistance for the following:
R(1) = 4, R(2) = 3, R(3) = 12
1/4 + 1/3 + 1/12
3/12 + 4/12 + 1/12 = 8/12
R(T) = 12/8 = 1.5 ohms
Series and Parallel Circuit
Diagram
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http://www.ndted.org/EducationResources/HighSchool/Elect
ricity/seriescircuit.htm
Charge Flow Direction: Direct
Current vs. Alternating Current
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Direct current - charges move in only one direction
 The type that is supplied by a battery or DC power supply
Alternating current
 Alternates its direction of motion
 It flows one direction during the first half
 Reverses direction in the second half
 Divided into cycles
 60 cycles per second in the US
 One full cycle is 1/60 second
 One half cycle is 1/120 second
 There are 60 cycles/second
 This is called a 60 Hertz AC
Examples of DC and AC
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http://www.pbs.org/wgbh/amex/edison/s
feature/acdc.html
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http://www.ndted.org/EducationResources/HighSchool/Electrici
ty/directcurrent.htm
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http://www.youtube.com/watch?v=JZjMuIHoB
eg&feature=player_detailpage#t=8s
http://www.youtube.com/watch?v=g17f9J1-rk&feature=related
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Other Circuit Components
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Capacitor
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A device that stores electrical charge until needed
Generally consists of two metal plates
 http://micro.magnet.fsu.edu/electromag/java/capacitance/in
dex.html
 http://micro.magnet.fsu.edu/electromag/java/capacitor/index
.html
Rheostat
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A device to vary resistance
Produces gradual changes in voltage or current flow
 http://micro.magnet.fsu.edu/electromag/java/filamentresista
nce/index.html
Electrical Power
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Measured in Watts
Watts = Volts X
Amperes