Topic 12 - Magnetism and the Motor effect

• What is a magnet?


  An object that produces a magnetic field.
• Unlike magnetic poles attract and like magnetic poles repel.
• What are the 3 magnetic materials?

  Iron, nickel, cobalt.
• What is the difference between a permanent and an induced magnet?

  Permanent: Retains magnetism without external influence. Induced: Becomes magnetic in the presence of a magnetic field.
• What is the structure of a magnetic field?

  1. Magnetic Field Structure:

  • Lines: Magnetic fields have lines of force.
  • Direction: From north to south outside the magnet.
  • Inside Magnet: South to north.

  1. Field Strength:

  • Closer Lines: Indicate stronger magnetic force.
  • Farther Lines: Indicate weaker magnetic force.

  1. Poles:

  • North Pole: Where magnetic field lines leave the magnet.
  • South Pole: Where magnetic field lines enter the magnet.
• You can use plotting compasses to show the shape and direction of the field of a magnet and the Earth’s magnetic field.

  
• The behavior of a magnetic compass is related to evidence that the core of the Earth must be magnetic. (The north of the earth is the magnetic south pole and the south of the earth is the magnetic north pole).
• What are some of the uses of magnetic materials?

  Electric motors, generators, transformers, magnetic storage devices (hard drives), MRI machines.
• When current flows around a long, straight conductor, it creates a circular magnetic field around it. Changing the direction of the current changes the direction of the magnetic field. The larger the current the closer you are, the stronger the field.

  
• What is the right-hand thumb rule?


  A rule that helps you depict the direction of a magnetic field when having the direction of the current.

  
• What is a solenoid?

  A coil of wire that produces a magnetic field when an electric current passes through it.
• Solenoid science:

  1. Inside the Solenoid:

  • Individual Coils: Each coil contributes a magnetic field.
  • Add Together: Fields from coils align and strengthen along the center.
  • Result: Strong, almost uniform magnetic field inside the solenoid.

  1. Outside the Solenoid:

  • Coil Arrangement: Magnetic fields outside vary in direction.
  • Canceling Effect: Fields from different coils partially cancel each other.
  • Result: Weaker overall magnetic field outside the solenoid.
• How can you increase the strength of a solenoid?

  Increase current or increase the number of turns in the coil or inserting a block of iron inside the coil.

  
• A current-carrying conductor placed near a magnet experiences a force and an equal and opposite force acts on the magnet.
• Magnetic forces are due to interactions between magnetic fields.
• What is Fleming's left-hand rule for?

  To find the direction of the force on a current-carrying conductor.
• What does each finger represent in Fleming's left-hand rule?

  ThuMb: Motion - The direction of the force

  First Finger: Field - The direction of the magnetic field

  SeCond finger: Current - The direction of the current in the wire.

  
• What is the motor effect?

  The motor effect is the phenomenon where a current-carrying conductor experiences a force when placed in a magnetic field.
• How do you find out the force using magnetic flux, current, and length?

  Force = B * I * L --- where B is the magnetic flux, current, and length.
• 1. Magnetic Interaction:

  • Conductor feels force in a magnetic field.

  1. Rule for Force:

  • Use Fleming's Rule to know force direction.

  1. Rotor in Motor:

  • Motor has a rotor with a coil.

  1. Force Causes Rotation:

  • Force on coil makes rotor turn.

  1. Rotor Keeps Turning:

  • Torque from force keeps rotor rotating.

  1. Motor's Purpose:

  • Rotor's spin drives the motor's job.
• What is the use of the split-ring commutator?

  To reverse the direction of current in a DC motor so that the motor keeps spinning in the same direction.