Physics

• Magnetism, Magnetic Forces and Magnetic Fields

  
• Magnetic phenomena were first observed at least 2500 years ago in fragments of magnetized iron ore found near the ancient city of Magnesia (now Manisa, in western Turkey)
• Poles


  Magnets have two poles: South and North

  
• Monopole/single pole of magnet doesn't exist. Magnets must and always have 2 two poles

  
• If a bar magnet is broken in two, each broken end becomes a pole
• Magnetic poles


  In contrast to electric charges, magnetic poles always come in pairs and can't be isolated. Breaking a magnet in two yields two magnets, not two isolated poles

  
• Magnets


  • Can exert forces on each other
  • Alike poles repel each other
  • Unlike poles attract each other

  
• Object that contains iron but is not itself magnetized (shows no tendency to point north or south)

  Is attracted by either pole of a permanent magnet
• Magnetic field


  An area wherein an object experiences a magnetic force

  
• Magnetic field lines


  • The magnetic field is strong if the field lines are close to each other
  • Object is placed near the magnet, the object feels a strong magnetic field
  • Strength of magnetic field decreases as the distance of the object from the magnet increases

  
• Magnetic field lines of a bar magnet

  
• Magnetic field lines between unlike poles

  
• Magnetic field lines between like poles

  
• Earth's magnetic field


  Earth is a huge magnet itself, due to the Earth's magnetic field that aligns the needle of the compass

  
• Polarity of the Earth's magnet in the North and South


  • The South Pole of the Earth's magnet=Geographical North of the earth
  • North Pole of the Earth's magnet=Geographical South

  
• Magnetic declination/Magnetic variation


  The axis of the Earth's magnetic field and the geographical axis do not coincide with each other, so a compass reading deviates somewhat from geographic north. This deviation, which varies with location, is called magnetic declination or magnetic variation

  
• Magnetic effect of electric current

  
• Electromagnetism


  Hans Christian Oersted discovered that when a compass is placed near a wire, the compass needle deflects if (and only if) the wire charges an electric current. He then concluded that an electric current produces a magnetic field

  
• Permeability of free space

  μo, a proportionality constant
• SI unit of magnetic field

  • 1 tesla = 1T = 1 newton/(coulomb) (meter/second)
  • 1 tesla = 10^4 gauss
  • 1G=10^-4T

  
• Magnetic force on a current-carrying conductor

  The force is always perpendicular to both the conductor and the magnetic field, with the direction determined by the same right hand rule we used for a moving positive charge

  
• Magnetic field vector


  Just as an electric field surrounds an electric charge, a magnetic field surrounds a magnet

  
• Magnetic field


  • Region of space where a magnet is capable of exerting force on a magnetic material
  • Can be defined in terms of the force exerted on an electric charge moving in the field
  • Has direction, the direction of the magnetic field at a given location can be defined as the direction that the north pole of a compass needle would point if placed at that location
  • Composed of lines of forces and these lines point from the North pole to South pole

  
• Solenoid

  A device that is a long, straight wire that is bent into a coil of several closely spaced loops, often called an electromagnet. This device is important in many applications because it acts as a magnet only when it carries a current and effectively has a north and south pole

  
• Magnetic force on a moving charge

  When a charge is placed in a magnetic field, it experiences a force, provided that: 1) The charge must be moving, because no magnetic force acts on a stationary charge, and 2) The velocity of the moving charge must have a component that is perpendicular to the direction of the magnetic field

  
• Motion of charged particles in a magnetic field

  The magnetic force acting on the charge is always directed toward the center of the circle, causing a centripetal acceleration that changes only the direction of the velocity and not its magnitude