Electric and Magnetic Fields

D2

Coloumb’s Law: Can be used to calculate the force between two charges

The relative permittivity εr for a medium other than a vacuum or air is defined as the ratio between the permittivity of the medium ε and the permittivity of free space ε0:

Electric dipole positive and negative charge (has to be equal magnitude but opposite in sign)

Field strength is the amount of force per unit charge

Electric field:

  • Electron moves in the opposite direction

  • the total electric charge within an isolated system remains constant over time.

  • Charge flows in between conductors until they have the same electric potential

Parallel Plates:

  • Are positively and negatively charged plates separated at some distance

  • The electric field between a parallel plate is always constant, therefore the force is always constant

  • Field is uniform in the middle and the horizontal components cancel each other to form a vertical electric field

  • However the electric fields become weaker and weaker and non uniform at edges

Milikan experiment:

  • Figured out the elementary charge of an electron and its mass

  • Found mass of the oil droplet then turned electric plates in order to reduce veloicty

Creation and destruction of magnetic fields:

  • Move one pole of a magnet over the material many times.

  • Place material in a strong magnetic field

  • Pass a constant electric current through the material

  • Can unmagnetized them by heating them above the curie temperature

  • or Physically disrupt the aligned domains with force

Domain Theory:

  • states all materials are made up of tiny regions or domains that act and behave as a mini-magnet inside the material. If they are aligned they will become magnetized if random they cancel each other out

Magnetic Field B:

  • A Magnetic Field B is the region of space around a magnet where another magnet or magnetic material will experience a force.

  • Is measured in Teslas

  • A compass is designed and engineered to always follow the magnetic field lines and point towards the South pole of a magnet (Lines leaving north pole and entering the south pole

  • Strength is determined by the density of field lines The field lines never touch or cross each other’

Hand Rules:

  • Use right hand for current or positive charges

  • Use your left hand for electron flow

  • Current Carrying wire

    • Place the thumb in the direction of the electric current.

    • The direction of the magnetic field curls with your fingers.

  • Solenoids

    • Curl fingers around the loops in the direction of the current.

    • Thumb will point to the North pole of the solenoid.

Field Lines:

  • Always originate from positive charges and terminate at negative charges

  • Number of lines is proportional to the charge

  • Perpendicular to the charge surface

Electromagnetism:

  • A current carrying wire will create a magnetic field of concentric circles surrounding the wire

  • An electron current flowing away from you produces a magnetic field that circulates in a clockwise direction

  • An electric current flowing towards you produces a magnetic field that circulates in a counter clockwise direction