Electromagnetism

• It is always associated with charges in motion.

  Magnetic Field
• The current supplies a _____________ that increases with the amount of current.

  Magnetizing force or Magneto Motive Force (mmf)
• It produces a flux density that increases with the permeability of the

  medium.

  Field Intensity (H)
• With a coil magnet, the ________ depends on how many current flows in

  the turns of the coil.

  Strength of the Magnetic Field
• It specifies the amount of magnetizing force or magnetic potential

  Quantity IN
• The CGS unit of mmf is _________.

  Gilbert (Gb)
• An English scientist who investigated the magnetism of the Earth

  William Gilbert
• One ampere-turn is equal to __________.

  1.26 Gb
• I x N = mmf
• It depends on how long the coil is.

  Field Intensity (H)
• The field intensity for a solenoid is at the ___________.

  Center of an air core
• The field intensity for a iron core is at the ___________.

  Through the entire core
• The CGS unit for H is _________.

  Oersted (Oe)
• A Danish physicist who discovered electromagnetism was Hans Christian Oersted
• The unit for field intensity (H)

  Ampere – turns per meter
• Formula for Field intensity (H)

  H = mmf/l
• Formula of Permeability

  μ = B/H
• It is often used to show how much flux density (B) results from increasing

  the amount of field intensity (H).

  B – H Curve
• The current in the coil equals to ________.

  V/R
• The field intensity (H) increases with _________.

  Higher IN
• The __________ depends on the field intensity (H) and permeability of the iron.

  Flux Density (B)
• The effects of little change in flux density when the field intensity

  increases.

  Saturation
• It means “a lagging behind”.

  Hysteresis
• The flux ________ the increases or decreases in magnetizing force.

  Lags
• The energy wasted in heat as the molecular dipoles lag the magnetizing

  force

  Hysteresis Loss
• It is actually a B – H curve with an AC magnetizing force

  Hysteresis Loop
• The value of flux density in which is residual induction of a magnetic

  material.

  Retentivity
• The value of -HC, which is equals the magnetizing force that must be

  applied in the reverse direction to reduce the flux density to zero.

  Coercive Force
• The method of demagnetization

  Degaussing
• The faster the magnetizing force changes, however, the

  greater the hysteresis effect.
• To demagnetize a magnetic material completely, the residual induction B R must be reduced to zero.
• He found that current in a wire could move a magnetic compass needle.

  Oersted
• A magnetic field in motion forces electrons to move, producing ___

  Current
• The Henry unit of inductance is named after __________.

  Joseph Henry
• The farad unit of capacitance is named after __________.

  Michael Faraday
• It combines effect of an electric current and magnetism

  Electromagnetism
• The magnetic lines are ________, as the field is symmetrical with respect to the wire in the center.

  Circular
• The magnetic field with circular lines of force is in a _____________ to the current in the wire.

  Plane Perpendicular
• If you look along the wire in the direction of electron flow, the magnetic

  field is ___________

  Counterclockwise
• The opposite direction of electron flow produces a ___________.

  Reversed Field