topic 12 - magnetism

• What is an electromagnet?

  A solenoid with an added iron core
• How does adding an iron core affect an electromagnet?

  It increases the strength of the magnetic field
• What rule determines the force produced by the motor effect?

  Fleming’s Left-Hand Rule
• What is the motor effect?

  A force between a magnetic field and a current-carrying conductor
• What does the second finger represent in Fleming’s left-hand rule?

  The direction of current flow in the conductor
• What factors affect the size of the force on a current-carrying wire?

  The magnitude of the current and magnetic field strength
• What does the thumb represent in Fleming’s left-hand rule?

  The direction of the force produced
• What does the forefinger represent in Fleming’s left-hand rule?

  The direction of the magnetic field
• What happens to the force if the strength of the current is increased?

  The strength of the force is increased
• What happens to the force if the direction of current is reversed?

  The direction of the force is reversed
• What is the equation linking force, magnetic flux density, current, and length?

  F = BIL
• What criteria must be met for the force equation to hold?

  The conductor must be at right-angles to the magnetic field
• What is the unit used for magnetic flux density?

  Tesla, T
• How does an electric motor work?

  A coil in a magnetic field experiences forces causing rotation
• What happens if the current and magnetic field are parallel?

  No force will act
• What type of force is exerted by like poles of a magnet?

  A repulsive, non-contact force
• What type of force is exerted by unlike poles of a magnet?

  An attractive, non-contact force
• How are electric motors kept rotating?

  A split ring commutator switches the current direction
• Where are the magnetic forces strongest on a magnet?

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

  They exert a force on each other
• What is a magnetic field?

  The region where a magnet exerts a force
• What is the difference between a permanent magnet and an induced magnet?

  A permanent magnet produces its own field; an induced magnet becomes magnetic in a field
• What type of force does induced magnetism always cause?

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

  It loses most/all of its magnetism
• How does the strength of a magnetic field change with distance from the magnet?

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

  From north pole to south pole of a magnet
• What can be said about the force between a magnet and a magnetic material?

  It is always attractive
• What does a magnetic compass contain?

  A small bar magnet that points to Earth's magnetic field
• 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 indicate a strong or weak field?

  Strong
• What is produced when current flows through a conducting wire?

  A magnetic field is produced around the wire
• True or false: Do magnetic field lines ever cross each other?

  True; they never cross, touch, or overlap
• How is a plotting compass used to map out a magnetic field?

  1. Place a compass near the field
  2. Draw an arrow in the direction it points
  3. Repeat at different points
  4. Join arrows to create a field pattern
• Describe the magnetic field found inside a solenoid.

  Strong and uniform
• What is a solenoid?

  A coil of wire creating a strong magnetic field
• Is the magnetic field outside a solenoid strong or weak? Why?

  Weak; fields from each coil cancel out