Electromagnetism

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Electromagnetism
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Historical Background

• Earliest studies of electricity
• Charges could be induced to move but only in a
  sudden discharge
• 1700
• Discovery of battery (constant flow of
  electricity)
• 1820
• Oersteds Experimnet

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Oersteds Experiment

• Any charge in motion induces a magnetic field
• A charge at rest produces no magnetic field

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Solenoid

• A coil of wire.

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Electromagnetic

• A coil of wire with an iron (ferromagnetic) core
• Advantage of and Electromagnet
• Magnetism can be turned on and turned off

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Laws of Electromagnetic Induction

• Faradays Law (1st law)
• An electric current is induced to flow in a
  circuit if some part of that circuit is in a
  changing magnetic field.

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Electromagnetic Induction

• Move the conductor
• Move the wire through the magnetic field
• Move magnetic lines of force
• Move the magnetic field across the wire
• Vary the magnetic flux strength
• Through a stationary wire vary the strength of
  the current so that it increases and decreases

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The strength of the induced current depends of 4
factors

• Strength
• Of the magnetic field
• Speed
• Of the motion betweens the magnetic fields and
  the conductor
• Angle
• Between the magnetic fields and the conductor
• Number of turns
• In the conducting coil

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2nd Law of Electromagnetism

• Lenzs law
• The induced current flows in a direction that
  opposes the action that induces it.

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Types of Induction

• Mutual induction
• Inducing a current flow into a secondary coil by
  placing it in the varying magnetic field lines
• Self Induction
• When a current is induced due to the construction
  of the electromagnet

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Electric Generator

• Converts mechanical energy to electrical energy
• Composed of a loop of wire (armature) placed
  between 2 magnets of opposing poles
• Movement of the armature through the magnetic
  field lines causes a current to be induced in the
  wire.
• Produces Alternating Current (AC)

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Direct Current Generators

• Constructed similar to AC generators with the
  addition of a commutator ring
• Commutator ring acts as a switch to reverse the
  negative current to positive current.

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Electrical Motors

• Converts electrical energy into mechanical energy
• Composed of the same elements as a generator
  except that a current is applied to the wire
  which creates a small magnetic field and causes
  the wire to move.

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Induction Motor

• Composed of several external electromagnets
  (stator) with a fixed internal loop of wire
  (rotor)
• Utilized in the rotor of the x-ray tube

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Transformer

• Transforms electric potential and current into
  higher and lower intensities
• Can only be used with Alternating Current

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Transformer Law

• As the number of turns on the primary side
  increases so does the voltage proportionally
• Vs Ns
• Vp Np

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Step up transformer

• Steps voltage up from a lower voltage to a higher
  voltage
• T he turns ratio is greater than 1
• 10/1
• 101

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Step down transformer

• Steps down voltage from higher to lower voltages
• The turns ratio is less than 1
• 1/10
• 110

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Transformer Effect on Current

• Current, voltage and the turns ratio is inversely
  proportional to one another
• Is Np Is Vp
• Ip Ns Ip Vs

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Reasons for transformer losses

• Resistance
• For every action there is an equal but opposite
  reaction
• Hysteresis
• The additional resistance created by alternate
  reversal of the magnetic field caused by the AC
  (also called lagging loss)
• Eddy currents
• Described by Lenzs law

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Types of Transformers

• Closed core transformer
• Square iron core with primary windings on one
  side and secondary windings on the other side
• Operates by means of mutual induction

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Types of Transformers

• Autotransformer (open core)
• Contains one coil of wire with an iron core which
  acts as primary and secondary windings
• Operates by means of self induction rather than
  mutual induction

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Types of Transformers

• Shell Type
• Composed of two closed iron cores which has one
  winding in the center of the two cores
• Operates by means of self induction

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The END