C3 Electricity

• Electric field lines:

  • moves from positive to negative
  • do not cross one another
  • number of lines proportional to magnitude of charge
• Conductors:

  • obey Ohm's Law - ohmic conductors
  • do not obey Ohm's Law - non-ohmic conductors
• Resistance, R : ratio of potential difference to current flowing in a component.

  V = I x R
• Ohm's Law: current flowing is directly proportional to the potential difference across a component provided temperature and other physical conditions remain constant.
• Electromotive Force (e.m.f) is the work done by an electrical source to move one coulomb of charge in a complete circuit.
• S.I unit for e.m.f is volt, V.
• Internal resistance, r is resistance within a dry cell.
• r, causes:

  • loss of energy as heat
  • pd lesser than emf
• Electrical energy & Power formulas:

  E = V x Q

  E = V x I x t

  Q = I x t

  E = P x t

  P = E / t

  P = ( V x Q ) / t
• Cost of electrical energy consumed = number of units x cost per unit