Revision Notes: Magnetism | Basic Electronics for SSS 1 PDF Download

Magnets

• Natural : found in nature (ex. Lodestone) – composed of oxides of iron (Fe₃O₄)-Attracts iron 
• Magnetism – property of attracting iron 
• Magnetic force- the force that a magnet exerts on iron  
• Artificial : magnetized piece of iron or magnetic materials.

Parts of bar magnet 

Magnetism

• Attractive property
  
• Directive property
  
• Poles exist in pairs ( No Monopoles exist)
  
• Like poles repel and Unlike poles repel each other
  

Repulsion is the Surer test for a Magnet 

Making Magnets 

• Magnetic Induction: Magnetism acquired by a magnetic material when it is kept near or in contact with a magnet. 
  
• Single Touch method: 
• Double Touch method:
  
  • Demagnetizing a Magnet : 
    • By hammering the magnet repeatedly 
    • By rough handling 
    • By heating and keeping in east west direction 
    • By passing AC current  
    • Self-demagnetization. 
  • Storing of Magnets : Magnet keepers
    
  • Uses of Magnet : 
    • Magnetic compass
    • Door bells 
    • Dynamos 
    • Motors 
    • Loudspeaker , etc., 
• Electrical method: It is a temporary strong magnet made from a piece of soft iron when current flows in the coil wound around it. It is an artificial magnet. The polarity and magnetic field strength can be changed. Demagnetized by switching off the current. 
  Strength depends on: 
  • Number of turns in coil 
  • Amount of current flowing 
• Uses: lifting and transporting huge mass of iron scrap, loading furnaces with iron, electric bell, electric fans, electric motors , etc.
• Electric Bell: Advantages of electromagnet :
  • Can be easily magnetized and demagnetized by turning the current on or off in the coil. 
  • They can be made stronger than any other permanent magnet. 
  • Poles of an electromagnet can be interchanged by reversing the direction of current.