Electric charges and fields

• The unit of electric charge is coulomb (C).
• The 3 properties of charge


  additive in nature

  quantized

  total charge in closed system is conserved
• what is electrification

  Method of charging a body
• 2 Methods of charging

  by friction

  by conduction
• what gets transferred when particles are rubbed against each other

  electrons
• charge carriers of metallic conductors

  electrons
• Apparatus used to detect electric charge on body

  gold leaf electroscope
• state coulombs law

  Coulomb’s law, the electrostatic force of attraction or repulsion between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. It acts along the line joining the two charges considered to be point charges.
• force acting along q1 due to q2

  F12
• force acting on q2 due to q1

  F21
• Coulombs law in vector form and explain terms

  $F21$

  
• q1q2>0 nature of charge?

  repulsive
• q1q2<0 nature of charge??

  attractive
• value of dielectric constant of vacuum

  K=1
• principle of superposition


  This principle states that the combined effect of force system acting on a particle or a rigid body is the sum of effects of individual forces.
• define electric field

  force experienced by a unit +ve charge
• is electric field scalar or vector


  vector
• SI unit of electric field

  N/C
• direction of electric field due to point -ve charge


  radially inward
• direction of electric field due to point +ve charge

  radially outward
• 3 properties of electric field lines

  they do not intersect

  do not form closed loops

  crowded in the region of stronger field and spaced apart in the region of weaker field
• defn of electric field lines

  pictorial way of representing electric field in a given region
• what is electric flux

  number of field lines of force passing normally through a surface area
• when is flux maximum and minimum

  max when tita = 0*

  min when tita = 90*
• define electric dipole

  pair of equal and opp charges separated by a small distance
• SI unit if electric flux

  Nm2C-1 or Vm
• define electric dipole moment

  product of magnitude of either charge or dipole length
• exp for torque in uniform electric field


  t=P x E
• when is torque max and min

  max tita=90*

  min tita=0*
• define linear charge density

  charge per unit length

  lambda=q\L
• define surface charge density

  charge per unit surface

  sigma=q/A
• define volume charge density

  charge per unit volume

  rho=q/V
• State gauss's law in electrostatics

  Gauss’s law in electrostatics states that the electric flux passing through a closed surface in air is equal to the 1/0ϵ0​1​ times total electric charge within the surface
• define gaussian surface

  the surface used to calculate electric flux and hence to apply gauss law