Electricity

• current?


  rate of flow of charge in a circuit
• 1 ampere is the current flow when 1 coulomb of charge passes a point each second
• potential difference is equal to the work done per coulomb of charge travelling in a circuit
• 1 volt is equal to 1 joule of work being done by each coulomb of charge
• an ideal voltmeter has infinite resistance and so no current is drawn from the circuit
• resistance is a measure of how difficult it is for a current to flow ina circuit
• resistance is directly proportional to pd in a circuit and inversely proportional to current flow
• ohmic conductor is a conductor through which the current flow is directly proportional to potential difference when held at a constant temperature
• resistance of a material depends on

  cross sectional area, length and resistivity
• power?


  rate of energy transfer
• 1 watt is the power dissipated when 1 joule of energy is transferred each second
• current is the same in all positions in series circuit
• potential difference over a loop is split between all components in ration of their resistance
• potential difference over each loop in parallel circuit is the same
• current in a parallel circuit is split between each branch and so is different in different parts of the circuit
• Kirchoff's first law?

  total current entering a junction is equal to the total current leaving it
• kirchoff's second law?


  sum of emf in any loop of a circuit is equal to sum of pd's of each component
• electromotive force?


  amount if energy supplied by the source per unit charge
• internal resistance?


  opposition to flow of charge within a cell
• eV?


  used to express very small energies derived from definition of p.d
• the energy gained by an electron travelling through a potential difference of one volt
• 1eV=1.6x10^-19 J
• when a charged particle is accelerated through a potential difference it gains kinetic energy
• if there are resistive forces energy will be lost from the system (dissipates) in the form of thermal energy. the system does work against the resistive forces
• (Ek+Ep at end)=(Ek + Ep at start)-(E lost)+(E put in)
• efficiency = (useful output power/input power) x 100
• Define non-ohmic?

  current is not proportional to potential difference applied. resistance is not constant
• examples of non ohmic devices?

  Diodes, filament lamp and thermistors.