Topic 12 - Magnetism and The Motor Effect

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

  poles of a 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?

  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 that a north pole would experience a force 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

  - the distance from the wire
• Does a high concentration of field lines mean the field is strong or weak?

  strong
• True of false: magnetic field lines never cross each other?

  True: they never cross, touch or overlap
• 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
• What is a solenoid?

  A coil of wire which when current passes through creates a strong magnetic field.
• Describe the magnetic field found inside a solenoid

  Strong and uniform
• Is the field on the outside of a solenoid strong or weak? Why?

  Weak.

  The fields from each coil cancel out, making the outside field weak.
• What is an electromagnet?

  ● A solenoid with an added iron core

  ● Adding the iron core increases the strength of the magnetic field
• What is the motor effect?

  When a force is exerted between a magnetic field and a current-carrying conductor placed in that field.
• What rule is used to determine the force produced by the motor effect?

  Fleming's left hand rule
• When using Fleming's left hand rule what does the forefinger represent?

  The forefinger points in the direction of the magnetic field.
• When using Fleming's left hand rule what does the second finger represent?

  The second finger points in the direction of current flow in the conductor.
• When using Fleming's left hand rule what does the thumb represent?

  The thumb points in the direction of the force produced by the motor effect.
• What factors affect 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, what happens to the force?

  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, what happens to the force?


  The strength of the force is increased.
• Give the equation linking force, magnetic flux density, current and length

  Force (N) = Magnetic flux density (T) x Current (A) x Length (m)

  
  

  F = BIl
• What criteria must be met 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.
• What is the unit used for magnetic flux density?

  Tesla (T)
• If the current and the magnetic field are parallel to each other, which direction would the force act in?

  No force will act
• How does an electric motor work?

  ● A coil of wire, carrying a current, is placed in a magnetic field

  ● The forces on the two sides perpendicular to the field experience forces in opposite directions

  ● This causes a rotational effect
• How are electric motors kept rotating?

  A split ring commutator is used. This switches the current direction every half turn, which ensures that the coil keeps spinning