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DC Current Electricity and
Magnetism in
Electrical Conductors
Electric FieldAn 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.
•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.
Current Electricity
Electric Fields Drive Current Electricity
Conventional Current
Assumes Charge Flows from Positive to Negative
CationAnion
Ions contain CHARGES that create electric fields
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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. These opposite electric fields produce imbalanced forces necessary
to move the charges through the circuit.
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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,
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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When current moves through a conductor a circular magnetic field is induced around the conductor
Magnetic Field LinesDirecti
on of Conventio
nal Curre
nt
Negative Battery TerminalPositive Battery
Terminal
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.
The Direction and Motion of an Induced Magnetic Field in a Conductor
Current Coming Towards You
Current Moving Away From You
X
When current moves through a coiled conductor a circular magnetic field is induced about the coil
Current and Magnetism in a Coil
Motor (armature) rotation is caused by the simultaneous attraction and repulsion between the electromagnetic
field in the armature and a fixed magnetic field
Fixed Magnets
Armature
Induced Magnetic Field (Due to current)
Fixed Magnetic Field
Force
A Conductor in a Fixed Magnetic Field
A Current Carrying Conductor in a Fixed Magnetic Field
NS
A Motor Armature in a Fixed Magnetic Field
The magnetic field surrounding a current carrying conductor interacts with an
existing magnetic field.
Direction of Force (Torque) acting to turn the Armature (Conductor)
Fleming's Left Hand (Motor) Rule
Determines the direction of DC current carrying conductor in a fixed magnetic field
Thumb = Direction of Conductor Motion Fore Finger = Direction of
Fixed Magnetic Field (N to S)
Middle Finger = Conventional Current Direction
Fleming's Left Hand (Motor) Rule
N
S
Direction of Rotation
Fixed Magnetic Field Direction
Conventional Current Direction
NS
N
S Use the Left Hand Rule to Determine the Rotation
Direction of the Armatures in A and B
Notice that when the current through the armature is reversed, it moves (Rotates) in the opposite direction
A
B
Hint: You will have to turn your left hand upside down for example A
Two parallel conductors carrying current in the same direction will attract each
other
Magnetic Forces Acting on Parallel Current Carrying Conductors
Magnetic Forces Acting on Parallel Current Carrying Conductors
X
Two parallel conductors carrying currents in opposite directions will repel each other, and they will set up a polarized magnetic field between themselves.
North
South
Magnetic Forces Acting on Parallel Current Carrying Conductors
X
South
North
South
NorthWrapping current carrying conductors around
an iron core creates an electro magnet
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
The End
