MAgnetic Field and Magnetic Force

• Magnet


  A material that produces a magnetic field and attracts magnetic materials

  
• Magnetic Field Lines


  Lines used to pictorially represent a magnetic field

  
• Magnetic Force Equation


  F = qvBsin(theta), where F is the magnetic force, q is the charge, v is the velocity, B is the magnetic field, and theta is the angle between v and B

  
• Magnetism


  • Universal characteristics of magnets:
  • Like poles repel, unlike poles attract
  • Impossible to separate north and south poles

  
• Magnetic Materials


  • Soft magnetic materials: easily magnetized but lose magnetization easily
  • Hard magnetic materials: used in permanent magnets
• Ferromagnets


  • Only certain materials like iron, cobalt, nickel, and gadolinium exhibit strong magnetic effects
  • Can be magnetized and become permanent magnets

  
• Ferromagnetic materials


  • Iron, cobalt, nickel, gadolinium, neodymium alloys
• Magnetite is a rock mineral and one of the main iron ores, with the chemical formula Fe3O4. It is ferrimagnetic.
• Magnetic Field Lines


  • Field is tangent to the line
  • Field strength is proportional to line density
  • Field lines cannot cross
  • Field lines are continuous loops

  
• Magnetic Force


  • Caused by current, the flow of charge
  • Magnetic fields exert forces on moving charges and other magnets

  
• Magnetic Field Units


  • SI unit is Tesla (T) or Weber per square meter (Wb/m^2)
  • CGS unit is Gauss (G), where 1 T = 10^4 G

  
• Direction of Magnetic Force

  Use right hand rule 1: point fingers in direction of velocity, curl towards magnetic field, thumb points in direction of force

  
• Magnetic force can supply centripetal force and cause a charged particle to move in a circular path of radius r = mv/(qB)

  
• Like poles (north-north or south-south) repel each other, while unlike poles (north-south) attract each other.
• A compass needle can be used to detect the presence of a magnetic field by aligning itself along the direction of the magnetic field lines.
• The strength of a magnetic field decreases with distance from its source.
• Right Hand Rule 2: Point your fingers in the direction of the current, curl your fingers toward the wire, and your thumb will point in the direction of the magnetic field
• Electric current produces a magnetic field around it according to Fleming's left-hand rule.
• Magnetic force is always perpendicular to vel

  ocity, so that it does no work on the charged particle.
• A charged particle having a velocity directed at an angle with a uniform magnetic field moves in a helical path
• Magnetic force can supply centripetal force and cause a charged particle to move in a circular path of radius:
• MagneAc poles always occur in pairs of north and south—it is not possible to isolate north and south pole
• The magnetic field is at its maximum value when the particle’s motion is perpendicular to the field. The magnitude of this maximum force is now: F = qvB
• The cgs unit for magnetic field is Gauss (G). 1 T = 10^4 G