Magnetic fields

• In Flemings left hand rule, the thumb stands for force, the first finger stands for field and the second finger stands for current.
• what does the right hand rule tell you?

  the direction of field around the wire in light of direction of wire/current
• A magnetic field is caused by moving charges
• What does the symbol B stand for?

  magnetic field
• What is force directly proportional to?

  F is directly proportional to the magnetic field, the current in the wire and the length of wire inside the magnetic field
• F = B x I x L
• Something is magnetic when all of their magnetic moments align, there is a net magnetic moment
• Materials may have magnetic atoms inside, but won’t be magnetic as their magnetic moments face different directions and so don’t have a NET magnetic moment
• Field lines run from N to S
• The earths geographical North Pole is actually the south pole, which is why the finding north in a compass points towards ’north’
• lines of flux must be complete loops
• A stronger field means that there is a higher flux density (compacted field lines)
• a static charge causes an electric field
• A moving charge caused a magnetic and electric field : elecromagnetic field
• Ferro magnetic materials have their magnetic moments naturally aligned (Iron Fe, Cobalt Co, Nickel Ni)
• the delocalised electrons moving inside material create the magnetic moments
• You can create magnetic fields by aligning magnetic moments or by the movement of of electrons
• Can create a magnetic field with a current flowing through a circuit as?

  there are moving electrons (from the negative pole to positive pole in a conventional current circuit)
• North to south outside of the magnet
• Magnetic field lines are also known as lines of Flux
• Flux is a measure of magnetic field, measured in W Webers with the symbol Phi
• Flux density has the symbol B, and measured in Teslas T, or Webers per metre squared. it is how much flux per area.
• When a magnetic field and a current carrying wire interact, the field lines are distorted.
• When the field lines of magnetic field and charge carrying wire are in same direction?

  the force of field combines and you have a stronger field
• When field lines of magnetic field and charge carrying wire are opposite directions?

  the fields cancel eachother out, the field is weaker in that section
• the charge carrying wire can experience a force when in a magnetic field due to?

  unbalanced fields; there is a net field so there is a net force.
• The direction of the force created when charge carrying wire is in a B us dependent on?

  direction of current and direction of B
• What has the symbol, B?

  magnetic field or flux density
• Faradays 1st law?

  Induce emf by changing flux linkage
• faradays second law?

  emf proportional to number of loops multiplied by change in flux linkage over change in time
• Lenz’s law?


  Emf = - N (change in flux linkage/ change in time)
• The motor effect is when a current carrying wire in a magnetic field will experience a force, due to?

  it creating its own magnetic field (moving charge) that interacts with the other. Unbalanced fields leads to unbalanced forces.
• Right hand rule shows current in the wire with surrounding field OR the North pole with surrounding current
• Unit for magnetic flux density, B is Tesla
• F = B I L only works when current and field lines are perpendicular to eachother
• When wire is parallel to field lines there is no force
• flemmings LHR, thumb is force, first finger is field second finger is current
• Practical for finding magnetic flux density is the blue tack on aluminium foil
• Free charged particles moving perpendicular to magnetic field also experience a force (perpendicular to velocity)
• F = B Q V