Chapter 14: Electromagnetism - Oakton
Transcript of Chapter 14: Electromagnetism - Oakton
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Chapter 14: Electromagnetism
Version 0.51
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Electromagnetism
An electrical current in a wire produces a magnetic field
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Ampere-Turns
The strength of the magnetic field in a coil depends on
Magnitude of the current
Number of turns
Known a the magnetomotive force (mmf)
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MMF Formula
MMF = I x N
MMF – magnetomotive force in Amp-turns
I – current in ampreres
N – number of turns in a coil
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Amp - turn Examples
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Field Intensity
Defined as H
Mmf per unit length
Amp-turns of mmf ÷ length of coil
Unit is the amp-turns per meter.
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MMF Examples
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Magnetic Polarity
Depends
Flow of the current
Direction of the coil winding
Reversing either changes the polarity of the coil
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Coil Magnetic Polarity
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Induced Current
When magnetic flux moves across a conductor it forces free electrons in a coil to move, creating electrical current
Induction
Conductor must be perpendicular to the magnetic flux
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Magnetic Induction
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Faraday’s Law
Amount of induced voltage depends on:
Amount of magnetic flux
Number of turns
Rate of change in the magnetic flux
Faster the flux changes the greater the induced voltage
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Faraday’s Law Formula
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Relay
Electromechanical device
Operates by induction
Use coil to operate a set of contacts
NC or NO
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Relay Diagram
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Relay Contacts
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Typical Relays
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Typical Relays
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Relay Applications
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Relay Specifications
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Contactors
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Motor Starter