♡ Topic 12_Magnetism and the motor effect ♡

• At which part of a magnet are the magnetic forces strongest?

  The poles of the magnet.
• What happens when two magnets are brought close to each other?

  They exert a force on each other.
• What type of force is exerted if two like poles of a magnet are brought near each other?

  A repulsive, non-contact force.
• What type of force is exerted if two unlike poles of a magnet are brought near each other?

  An attractive, non-contact force.
• What is a magnetic field?

  The region surrounding a magnet where another magnet or magnetic material experiences a non-contact force.
• What is the difference between a permanent magnet and an induced magnet?

  • A permanent magnet produces its own magnetic field
  • An induced magnet becomes magnetic when placed in a magnetic field
• Induced magnetism always causes what type of force?

  A force of attraction.
• What is the effect when an induced magnet is removed from a magnetic field?

  The induced magnet loses most/all of its magnetism.
• Give four examples of magnetic materials.

  1. Iron

  2. Steel

  3. Cobalt

  4. Nickel
• What can always be said about the force between a magnet and a magnetic material?

  It is always attractive.
• How does the strength of a magnetic field alter as you move further away from the magnet producing it?

  The magnetic field strength decreases the further you move away.
• In what direction does a magnetic field point?

  • In the direction of the force that a north pole would experience if placed in the field
  • From the north seeking pole to the south seeking pole of a magnet
• What does a magnetic compass contain?

  A small bar magnet that points in the direction of the Earth’s magnetic field.
• What is produced when current flows through a conducting wire?

  A magnetic field is produced around the wire.
• What determines the strength of the magnetic field around a current-carrying wire?

  The magnitude of the current flowing through the wire.
• Does a high concentration of field lines mean the field is strong or weak?

  Strong
• True or false: magnetic field lines never cross each other?

  True; they never cross, touch or overlap.
• An electromagnet is a solenoid with an added iron core, which increases the strength of the magnetic field
• How is a plotting compass used to map out a magnetic field?

  • Place a compass (containing a needle magnet) on a piece of paper near the field
  • Draw an arrow in the direction the compass points
  • Repeat at different points on the paper
  • Join the arrows to make a complete field pattern
• The motor effect is when a force is exerted between a magnetic field and a current-carrying conductor placed in that field
• What is a solenoid?

  A coil of wire which when current passes through creates a strong magnetic field.
• Fleming’s Left-Hand Rule is used to determine the force produced by the motor effect
• Describe the magnetic field found inside a solenoid.

  Strong and uniform.
• When using Fleming’s left hand rule:

  • The forefinger represents the direction of the magnetic field
  • The second finger represents the direction of current flow in the conductor
  • The thumb represents the direction of the force produced by the motor effect
• Is the field on the outside of a solenoid strong or weak? And why?

  Weak.

  The fields from each coil cancel out, making the outside field weak.
• Factors affecting the size of the force on a current-carrying wire in a magnetic field:

  • The magnitude of the current flowing through the conductor
  • The strength of the magnetic field that the conductor is placed in
• If the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, the direction of the force is reversed
• If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, the strength of the force is increased
• The equation linking force, magnetic flux density, current, and length is:

  force (N) = magnetic flux density (T) x current (A) x length (m)

  F = BIL
• Criteria for the equation linking force, magnetic flux density, current, and length to hold:

  The conductor must be at right-angles to the magnetic field it is placed in
• The unit used for magnetic flux density is Tesla, T
• If the current and the magnetic field are parallel to each other, no force will act
• An electric motor works by:

  • Placing a coil of wire, carrying a current, in a magnetic field
  • The forces on the two sides perpendicular to the field experience forces in opposite directions, causing a rotational effect
• Electric motors are kept rotating using a split ring commutator, which switches the current direction every half turn to ensure the coil keeps spinning