motor effect

• label

  A) upward

  B) downward

  C) +

  D) -

  E) dc motor

  F) split ring commutator

  G) direction

  H) current

  
• • The motor effect occurs when a wire with current flowing through it is placed in a magnetic field and experiences a force
  • This effect is a result of two interacting magnetic fields
  • One is produced around the wire due to the current flowing through it
  • The second is the magnetic field into which the wire is placed,for example,between two magnets
  • As a result ofthe interactions ofthe two magnetic fields,the wire will experience a force

  
• Current flowing in coil @ 90 to direction of magnetic field:

  • current creates magnetic field around coil
  • magnetic field produced around coil interacts with field produced by magnets -> force exerted on the coil
  • direction of force can be determined using Fleming's left-hand rule
  • As current flow in opposite directions on each side of coil, force produced from magnetic field will push one side of coil up, other side down -> rotate until in vertical position
  • When the coil is in the vertical position there will be a force acting upwards and a force acting downwards

  
• • The split ring commutator swaps the contacts ofthe coil
  • This reverses the direction in which the current is flowing
  • Reversing the direction ofthe current will also reverse the direction in which the forces are acting
  • As a result, the coil will continue to rotate
  • The commutator reverses the direction ofthe current in the coil every half turn This will keep the coil rotating continuously as long as the current is flowing
• CURRENT ALWAYS FLOWS FROM POSITIVE TO NEGATIVE

  A) upward

  B) downward

  C) direction

  
• Factors Affect ing the D.C Motor

  • speed of coil rotation can be increased by:

  1. Increasing the current
  2. Increasing the strength ofthe magnetic field

  • The direction of rotation of coil in the d.c motor can be changed by:

  1. Reversing the direction ofthe current
  2. Reversing the direction ofthe magnetic field by reversing the poles ofthe magnet

  • The force supplied bythe motor can be increased by:

  1. Increasing the current in the coil
  2. Increasing the strength ofthe magnetic field
  3. Adding more turns to the coil
• LOUDSPEAKERS

  • Loudspeakers, headphones convert electrical signals -> sound (motor effect)
  • coil of wire wrapped around a pole of permanent magnet
  • alternating current passes thru the coil -> changing magnetic field around coil which interacts w field from permanent magnet
  • this exerts a force on coil which constantly changes direction
  • this makes the coil oscillate which causes the speaker cone to oscillate
  • This makes the air oscillate, creating sound waves

  
• • changing frequency of ac supply = frequency that cone vibrates = pitch
  • size of current = amplitude of vibration = volume
• label

  A) clockwise

  B) coil

  C) magnet

  D) ^

  E) v

  
• Factors Affecting Magnetic Force

  • Magnetic forces r frm interactions btwn magnetic fields: stronger fields produce stronger forces, vice versa
  • increasing force

  1. amt of current flowing thru the wire: increases magnetic field around wire
  2. Using stronger magnets: increases magnetic field btwn poles ofthe magnet
  3. Placing the wire at 90 to the direction ofthe magnetic field lines between the poles ofthe magnet: maximum interaction between the two magnetic fields

  • If the two magnetic fields are parallel there will be no interaction between the two magnetic fields and therefore no force produced