physicsss

• Magnetism


  A material that attracts iron and some other metals. When two magnets interact, they can either attract or repel each other depending on their orientation.

  
• Magnetic poles


  • Magnets have two regions called magnetic poles where the attractive and/or repulsive interactions are the strongest. The two different poles of a magnet are called north and south, after the geographic designations.

  
• Composition of a magnet

  
• If the poles are opposite

  They attract each other
• If poles are the same


  They repel each other
• If you cut a magnet into two pieces, then the result is two magnets. If you divide those magnets, you end up with four magnets.
• You cannot divide the north from the south pole, because even an individual electron can behave like a tiny magnet with a pair of poles.

  
• An electron cannot be divided, so this means that magnetic poles always come in pairs.
• Magnetic force


  The noncontact force that arises between moving electric charges.

  
• Magnetic moment

  A vector that represents the strength and orientation of a magnet. The head of the vector represents the north pole, and the tail represents the south pole.

  
• Types of Magnetic Materials

  • Permanent magnets (ceramics, rare-earth metals, iron alloys containing aluminium, nickel, and cobalt)
  • Ferromagnetic materials

  
• Ferromagnetic materials

  Materials that exhibit magnetic effects, but only in the presence of magnets. Their atoms exhibit magnetic moments, but in random orientations, requiring the influence of a magnet to align.

  
• Magnetization

  The process of aligning the magnetic moments in a ferromagnetic material

  
• Magnetic domains


  Large groupings of similarly aligned magnetic moments that form naturally in ferromagnetic materials.

  
• Magnetizing a Ferromagnet


  1. Placing it between the opposite poles of two permanent magnets

  2. Heating or hitting the material
• Magnetic field


  A vector field that describes a material's magnetic influence throughout space.
• Earth behaves as a giant magnet, and as a result is surrounded by a magnetic field.
• Magnetic declination


  The horizontal angle between true north (the direction to the geographic pole) and magnetic north (the direction a magnetic compass would point).

  
• Modeling multiple magnets


  At each point in space, imagine a compass. Sketch the direction the compass would point due to the presence of one magnet. Then, sketch the direction it would point due to the other magnet. The compass will actually point somewhere in between those two directions, depending on the strength of the field from each magnet.

  
• The resultant field located at point P points more in the direction of magnet B's field because it is closer to magnet B. The resultant field at point Q is zero, so an actual compass needle would be unstable and could point in any direction.

  
• The magnetic field between the like poles of two equal-strength magnets is found using superposition.

  
• Magnetic force from moving charges


  Magnetic force is the result of an interaction between moving charges. Moving charges generate magnetic fields.

  
• The magnetic field around a wire forms circles around the outside of the wire, while the field around a coil of wires is similar to the field around a bar magnet.

  
• Lorentz force equation


  The mathematical representation of the total force on a charged particle, including both the electric and magnetic force.

  
• Right-hand rule


  Used to determine the direction of the magnetic force on positive charges.

  
• Left-hand rule


  Used for negative charges.
• Charged particles in magnetic fields

  A charged particle in a uniform magnetic field will experience a centripetal force and move in a circular path. A charged particle with a velocity that is at a nonperpendicular angle to a uniform magnetic field will move in a helical path along the direction of the field lines.

  
• The force on a current-carrying wire is proportional to the current, the magnetic field, and the length of wire in the field.
• Only the length of the wire that is perpendicular to the field will contribute to the force, because only the component of the current direction perpendicular to the magnetic field produces a magnetic force.
• Torque


  Forces applied at different locations on an extended system can cause rotational motion. A lever arm is the distance from the axis of rotation to the point where the force is applied, and it is perpendicular to the axis of rotation. Therefore, a torque is produced on each side of a loop of wire in a uniform magnetic field when a current travels through the loop.
• Force on a wire


  Proportional to the current, the magnetic field, and the length of wire in the field
• Modelling the Force on a Wire

  1. Only the length of the wire that is perpendicular to the field will contribute to the force

  2. The component of the current direction perpendicular to the magnetic field produces a magnetic force

  
• Torque


  Forces applied at different locations on an extended system can cause rotational motion
• Torque on Loops


  1. Current travels through the loop in opposite directions on either side

  2. Forces act on the opposite sides in opposite directions

  3. Lever arm is present due to the separation of the force application points

  4. Net torque causes the loop to rotate
• Modelling Rotations


  1. Draw an extended free-body diagram for the loop

  2. Analyse the various torques produced

  3. Model for multiple orientations of the loop as it rotates
• When the lever arms decrease

  The torque decreases
• When the lever arms are at their maximum

  The torque is at its maximum
• When the lever arms are zero

  The torque is zero
• Mathematical model for net torque

  In terms of the lever arm and the force on each wire length
• Electric motors


  Most common application of magnetically induced torque on wire loops