Electromagnets Chapter 3.23

Electromagnets

• A solenoid wrapped around a soft iron core is an electromagnet
• The core amplifies the magnetic field produced by the electric current within the solenoid
• The magnetic field of the iron bar aligns with the current's field, increasing the overall field strength outside the solenoid
• The field quickly fades when the current stops as soft iron loses magnetism easily
• Electromagnets can be shaped like bars, horseshoes, or other formats
• They produce stronger fields than permanent magnets

Exercise 3.23

• If a current passes through a solenoid, an iron core approaching coaxially is attracted into the solenoid
• This illustrates magnetic induction

Applications of Electromagnets

• Tape Recorders: Use horseshoe electromagnets (tape heads) to magnetize metal-coated tape.
  • Small horseshoe electromagnets made of ferromagnetic material are magnetized permanently
• Erase Head: The first head on the recorder.
  • Used to demagnetize the tape for recording
  • High frequency alternating current (about 85 kHz) is used
  • Tape is driven at a constant speed through a gap between the magnetic poles of the electromagnets
  • Reversing the magnetic field of the electromagnet at the same frequency demagnetizes the tape

Exercise 3.24

• a) Magnetic Flux Pattern: Sketch the magnetic flux pattern of the electromagnet inside and near the gap.
• b) Overheating Tapes: Avoid overheating the tapes by [this section is incomplete or missing in the document]

The Electric Bell

• A continuous bell tone requires a mechanism to switch the current on and off rapidly.
• The diagram shows the automatic mechanism in an electric bell.
  • Components: Bell Push, Electromagnet, Springy Metal Strip, Contact Screw, Hammer, Gong