magnets and electromagnetic

• What are the two poles of a magnet called?

  North (N) and South (S)
• What happens when two magnets with the same poles are brought close together?

  They repel each other
• What occurs when two magnets with different poles are brought close together?

  They attract each other
• What type of force is exerted between a magnet and a magnetic material?

  Always attractive
• What is a magnetic field?

  Region around a magnet affecting other magnets
• How can a magnetic field be represented?

  By magnetic field lines
• What do magnetic field lines indicate?

  Direction of force on a north pole
• Which direction do magnetic field lines point?

  From north pole to south pole
• Where is the strength of a magnetic field greatest?

  At the poles of the magnet
• How does the distance from a magnet affect its magnetic field strength?

  It decreases as distance increases
• What does the closeness of magnetic field lines indicate?

  Stronger magnetic field
• What is a permanent magnet?

  Produces its own magnetic field
• What is an induced magnet?

  Becomes magnetic in a magnetic field
• What happens to an induced magnet when removed from a magnetic field?

  It loses most or all of its magnetism
• What does a magnetic compass contain?

  A small bar magnet
• What does an electric current flowing through a wire produce?

  A magnetic field around the wire
• What factors affect the strength of the magnetic field around a straight wire?

  Current size and distance from wire
• What effect does bending a wire into a solenoid have?

  Increases the strength of the magnetic field
• How can the strength of the magnetic field inside a solenoid be increased?

  By putting an iron core inside it
• What does Fleming's left-hand rule show?

  Direction of force, current, and magnetic field
• What is the symbol for magnetic flux density?

  B
• What unit is magnetic flux density measured in?

  Tesla (T)
• What is the motor effect?

  Force on a conductor in a magnetic field
• What causes the motor effect?

  Interaction between two magnetic fields
• What do loudspeakers and headphones do?

  Convert current changes to sound pressure variations
• What are the advantages of electromagnets?

  • Can be turned on and off
  • Strength can be adjusted by current
• How does an electric bell operate?

  1. Switch pressed, turning on electromagnet
  2. Iron armature attracted, hammer strikes gong
  3. Circuit breaks, electromagnet stops
  4. Armature springs back, cycle repeats
• What is the function of a circuit breaker?

  • Switch in series with electromagnet
  • Opens if current is too large
  • Turns off the current
• What is the principle behind electric motors?

  • Current-carrying coil rotates in a magnetic field
  • Split-ring commutator keeps direction consistent
• How does a moving coil loudspeaker work?

  • Coil in magnetic field experiences force
  • Diaphragm moves, creating sound waves
  • Frequency of sound matches current frequency
• What is the relationship between current and sound wave frequency in loudspeakers?

  • Frequency of sound wave equals frequency of current
• What happens to the diaphragm in a loudspeaker when the current changes direction?

  • Diaphragm moves in the opposite direction
• What is the role of the split-ring commutator in an electric motor?

  • Keeps the motor spinning in the same direction
• How can the speed of an electric motor be increased?

  • Increase current or magnetic field strength
• How can the direction of an electric motor's rotation be reversed?

  • Reverse current direction or magnetic field direction
• What is the effect of placing a conductor in a magnetic field?

  • It experiences a force due to the motor effect
• What is the relationship between the magnetic field and the current in a wire?

  • Current creates a magnetic field around the wire
• What happens to the magnetic field strength as the current increases?

  • The magnetic field strength increases
• What is the shape of the magnetic field around a straight wire?

  • Concentric circles at right angles to the wire
• What is the effect of distance on the magnetic field strength around a wire?

  • Magnetic field strength decreases with distance