electromagnets

• when a current flows through a conducting wire, a magnetic field is produced around the wire
• the strength of the magnetic field (around the wire with flowing current) depends on:

  • the size current through the wire (larger current = stronger field)
  • the distance from the wire (further = decrease)
• if we change the direction of the current, then we change the direction of the magnetic field
• solenoid: a coil of wire that increases the strengths of the magnetic field created by a current through a wire
• the magnetic field inside a solenoid is strong and uniform

  outside is similar shape to bar magnet
• increasing the strength of the magnetic field produced by a solenoid:

  • increasing the size of current
  • increasing the number of turns (of coils)
  • adding an iron core (= electromagnet)
• an electromagnet is a solenoid with an iron core

  these can be turned on or off
• if iron rods are in a solenoid and the switch is closed, why would they move apart?

  • rods become induced magnets
  • with the same polarity at each end