DC Current Electricity and Magnetism in Electrical Conductors

1
DC Current Electricity and
Magnetism in
Electrical Conductors
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Electric Field
An Electric Field or Force Surrounding a Charged
Particle
An electric field radiates outward from a
positive charge and radiates in toward a negative
point charge.
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Current Electricity

• The movement of Electric Charges is called
  Current.
• Current is measured by the amount of charge
  (Coulombs) passing through the cross-sectional
  area of a conductor in a given period of time
  (Seconds).
• A Conventional Current flows from a positive
  battery terminal to a negative battery terminal.

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Electric Fields Drive Current Electricity
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Conventional Current
Cation
Anion
Assumes Charge Flows from Positive to Negative
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Current Electricity
Batteries use electrochemical reactions to
produce dissimilar charges used to create current
in DC motors and circuits.
Ions contain CHARGES that create electric fields
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Current Electricity
The electric field produced in a battery forces
current through an electric circuit or conductor
connected across the battery poles,
Ions contain CHARGES that create electric fields.
These opposite electric fields produce imbalanced
forces necessary to move the charges through the
circuit.
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A current created by the unidirectional movement
of charge(s) through a conductor is called a
direct current. This current is produced by all
batteries
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Negative Battery Terminal
Positive Battery Terminal
Direction of Conventional Current
Magnetic Field Lines
When current moves through a conductor a circular
magnetic field is induced around the conductor
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The Right Hand Rule
The direction of the magnetic field surrounding
the conductor can be found using your
right hand
Position the thumb of your right hand pointing in
the direction of conventional current (Positive
to Negative) and your fingers will wrap around
the conductor in the direction of the induced
magnetic field.
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The Direction and Motion of an Induced Magnetic
Field in a Conductor
Current Coming Towards You
Current Moving Away From You
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Current and Magnetism in a Coil
When current moves through a coiled conductor a
circular magnetic field is induced about the coil
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Motor (armature) rotation is caused by the
simultaneous attraction and repulsion between the
electromagnetic field in the armature and a fixed
magnetic field
Armature
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A Conductor in a Fixed Magnetic Field
A Current Carrying Conductor in a Fixed Magnetic
Field
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A Motor Armature in a Fixed Magnetic Field
Direction of Force (Torque) acting
to turn the Armature (Conductor)
The magnetic field surrounding a current carrying
conductor interacts with an existing magnetic
field.
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Fleming's Left Hand (Motor) Rule
Thumb Direction of Conductor Motion
Fore Finger Direction of Fixed Magnetic Field
(N to S)
Middle Finger Conventional Current Direction
Determines the direction of DC current carrying
conductor in a fixed magnetic field
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Fleming's Left Hand (Motor) Rule
Direction of Rotation
Fixed Magnetic Field Direction
Conventional Current Direction
S
N
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A
Use the Left Hand Rule to Determine the Rotation
Direction of the Armatures in A and B
Hint You will have to turn your left hand upside
down for example A
B
Notice that when the current through the armature
is reversed, it moves (Rotates) in the opposite
direction
S
N
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Magnetic Forces Acting on Parallel Current
Carrying Conductors
Two parallel conductors carrying current in the
same direction will attract each other
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Magnetic Forces Acting on Parallel Current
Carrying Conductors
North
Two parallel conductors carrying currents in
opposite directions will repel each other, and
they will set up a polarized magnetic field
between themselves.
X
South
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Magnetic Forces Acting on Parallel Current
Carrying Conductors
South
South
North
North
Wrapping current carrying conductors around an
iron core creates an electro magnet
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The Armature of a Brush Commutated DC Motor is
made up of Current Carrying Conductors Wrapped
Around an Iron Core
The Motor Armature is an electro Magnet and
Operates according to the Principles Described in
this Slide Show
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End
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