rpc 5 prelims

• Magnetism


  - was discovered in Magnesia (what is now Western Turkey)

  -
• Magnetite


  an oxide of iron
• Lodestone (leading stone)


  a rod-like stone that, when suspended by string would rotate back and forth and pointed the way to water when at rest
• Magnetic Field of a Charged Particle

  perpendicular to its motion
• Lines of Magnetic Field

  can be bipolar or dipolar; meaning it always has a north and a south pole
• Magnetic Dipole


  small magnet created by the electron orbit
• Magnetic Domain


  the accumulation of many atomic magnets with their dipoles aligned
• Magnetic Permeability


  the ability of a material to attract the lines of magnetic field intensity
• Naturally Occuring Magnets


  - Earth

  - earth has a magnetic field because it spins on its axis

  - lodestones in the Earth exhibit strong magnetism presumably because they have remained undisturbed for a long time within the Earth's magnetic field
• Permanent Magnets


  - available in many sizes and shapes

  - do not necessarily stay permanent

  - can be destroyed by heating / hitting with a hammer
• Electromagnets


  - consist of wire wrapped around an iron core

  - when an electric current is conducted through the wire, a magnetic field is created

  - the intensity of the magnetic field is proportional to the electric current

  - an iron core greatly increased the intensity of the magnetic field
• Nonmagnetic State


  - wood or glasss

  - unaffected by a magnetic field
• Diamagnetic State


  - water or plastic

  - weakly repelled from both poles of a magnetic field

  - materials cannot be artificially magnetized
• Paramagnetic state


  - gadolinium

  - weakly attracted to both poles of a magnetic field

  - materials are slightly attracted to magnet and loosely influenced by an external magnetic field

  - contrast agents used in MRI
• Ferromagnetic State


  - iron, nickel, or cobalt

  - can be strongly magnetized

  - materials can be magnetized by exposure to magnetic field
• Alnico


  - an alloy of aluminum, nickel, and cobalt

  - one of the more useful magnets produced from ferromagnetic materials
• Magnetic Susceptibility


  the degree to which a material can be magnetized
• Magnetic Laws


  - similar magnetic poles repel; dissimilar magnetic poles attract

  - the imaginary lines of a magnetic field leaves the north pole and enters the south pole of a magnet

  - magnetic poles are the ends of a magnet and are in pairs; the north and south pole.

  - the imaginary lines can be demonstrated by the action of iron filing near a magnet
• Magnetic Induction


  - a spinning charged particle will create a magnetic field along its axis of spin.

  - a moving charged particle will create a magnetic field perpendicular to that particles motion.

  - if a charged particle moves in a circular path, the perpendicular magnetic field also moves with the charged particle.
• Magnetic Induction


  - some materials such as ferromagnetic materials can be made magnetic by induction.

  - magnetic lines of induction are the imaginary lines of the magnetic field and its density is proportional to the intensity of the magnetic field.
• Hans Christian Oersted (Law of Magnetic Induction)


  - set out to show that electricity and magnetism are related.

  - moving or spinning electric charges should induce a magnetic field.-

  - used an electric circuit and a compass to prove his experiment.
• Faraday's Law by Michael Faraday (Law of Magnetic Induction)


  - 1st law of magnetic induction

  - an electric current is created in a circuit if some part of that circuit is in a changing magnetic field.

  - his experiments shows that magnetic fields can create electric currents

  - he showed the lines of a magnetic field by sprinkling iron filings on a piece of paper covering a magnet.
• Lenz's Law by Heinrich Friedrich Emil Lenz (Law of Magnetic Induction)


  - 2nd law of magnetic induction

  - an induced current within a conductive coil produces a magnetic field to oppose the change in magnetic field which produced it
• James Clerk Maxwell (Law of Magnetic Induction)


  - proposed that if a changing magnetic field can induce an electric field, then a changing electric field should induce a magnetic field

  - changing fields should move at a speed equal to the speed of light.

  - the magnetic force is proportional to the product of the magnetic pole strengths divided by the square of the distance between them.
• SI unit of Magnetic Field Strength

  Tesla
• Conventional Unit of Magnetic Field Strength

  Gauss
• 1 Tesla

  10,000 Gauss
• The Earth's Magnetic Field

  50 µT at the equator and 100 µT at the poles.
• Magnet used in an MRI System

  3 T
• Luigi Galvani (Electromagnetism Historical Development)


  observed that a dissected frog leg twitched when touched by two different metals as if it had been touched by two different metals (late 1700s).
• Alessandro Volta (Electromagnetism Historical Development)


  - questioned whether an electric current might be produced when two different metals are made into contact.

  - he succeeded in producing a feeble electric current using zinc and copper plates.

  - he stacked the copper-zinc plates to form a Voltaic pile to increase the current. This is the precursor to the modern battery.

  - each zinc-copper pile is called a cell of the battery.
• Modern Dry Cells


  use carbon rods as the positive electrode surrounded by an electrolytic paste housed in a negative zinc cylindrical can.
• Voltaic Pile


  it paved the way to the creation of modern batteries which is an example of sources of electric potential.
• Electric Potential is Measured

  in units of joule per coulomb or volt
• Solenoid


  a coil of wire with an electric current in it
• Electromagnet


  a current-carrying coil of wire wrapped around an iron core which intensifies the induced magnetic field
• Electromagnetic Induction


  - electric current is induced in a circuit if some part of that circuit is in a changing magnetic field.

  - no physical motion is needed.

  - if the current is increased in the electromagnet, the magnetic field will also change and induce a current in the coil.
• Faraday's Law


  the magnitude of the induced current depends on:

  - strength of the magnetic field.

  - velocity of the magnetic field as it moves past the conductor.

  - angle of the conductor to the magnetic field.

  - number of turns in the conductor.
• Electric Motors


  - electric current produces a mechanical motion.

  - motion of the compass needle.

  - has the same components as an electric generator.

  - electric energy is supplied to the current loop to produce motion.

  - uses many turns of wire for the current loop and many bars of magnets to create an external magnetic field.
• Electric Generators


  - mechanical motion induces electricity in a coil of wire.

  - the motion of a magnet near a coil of wire.

  - a coil of wire is places in a strong magnetic field between two magnetic poles.

  - the coil is rotated by mechanical energy which in turn induces an electric current.

  - the net effect of an electric generator is to convert mechanical energy into electrical energy.