current and circuits

• what is current 


  the rate of flow of charge
• what is a conventional current 


  the flow of positive charge from the positive terminal to the negative terminal
• what is the equation for current

  charge / time
• what is the equation for potential difference

  work done / charge
• each cell has a....


  positive terminal (high pd) and negative terminal (low pd)
• what is an electronvolt 


  the amount of energy needed to move an electron through a pd of one volt
• what can insulators conduct 


  static electricity by building up charge on its surface
• the transfer of energy between the collisions of free electrons result in...

  an increase in the kinetic energy of the atoms which raises the overall internal energy of the metal
• the greater the heating effect...

  the higher the resistance
• when are voltmeters and ammeters said to be ideal

  when a voltmeter has infinite resistance so no current passes through it

  when an ammeter has zero resistance so that all the current passes through it #
• what is the resistance of a component

  the ratio of the potential difference across the component to the current flowing through it
• what does resistance depend on 


  the material, the length and the cross-sectional area
• the resistance of a conductor is...

  directly proportional to its length and inversely proportional to its cross-sectional area
• what is resistivity 


  to resistance per unit length of a material with unit cross-sectional area
• when the diameter of the cross-section doubles...


  the area quadruples causing the resistance to drop by a quarter
• what is ohms law

  for a component at a constant temp, the current is proportional to the pd
• how do you calculate the resistance of an ohmic conductor

  the gradient of a I-V graph
• what are examples of a non-ohmic conductor 


  lamps, LED's and thermistors
• when the current in a semiconductor diode is in the direction of the arrowhead symbol it is...


  forward-biased meaning there is a sharp increase in current

  this is shown on the right side of the graph
• when the semiconductor diode is switched around...


  it doesn't conduct and is said to be reverse biased so the current through the diode is zero and is shown on the left side of the graph
• in a series circuit...

  the current is the same at any point

  the pd is split across all components
• in a parallel circuit...


  the total current is equal to the sum of the currents in each parallel branch of the circuit

  the pd is the same across each loop
• what happens when an electrical current does work against electrical resistance

  electrical energy is dissipated as thermal energy to the surroundings
• what are the factors that effect the amount of heat produced

  current and resistance
• what are the sources of electrical energy

  chemical cells, solar cells, mains electricity and wind generators
• how do solar cells convert electromagnetic radiation into electrical energy

  • light energy is transferred into thermal energy
  • the electrons absorb solar photons giving them enough energy to move and be released from the surface
  • these electrons transfer the thermal energy into electrical energy which is transferred to the external circuit
• what is an advantage of a single-use battery

  high energy density
• what is a disadvantage of a single-use battery

  high internal resistance
• what is an advantage of a mobile phone battery

  high electrical efficiency
• what is a disadvantage of a mobile phone battery

  expensive
• what is an advantage of a car battery

  low cost
• what is a disadvantage of a car battery 


  made from non-renewable materials
• what is an advantage of a solar cell

  unlimited supply of energy
• what is a disadvantage of a solar cell

  limited efficiency
• what is an advantage of a wind generator

  no chemical pollution
• what is a disadvantage of a wind generator

  noise/visual pollution
• what is an advantage of mains electricity

  high energy density
• what is a disadvantage of mains electricity

  produces pollution
• what is emf 


  the amount of chemical energy converted to electrical energy per coulomb of charge when charge passes through a power supply
• what is another way of describing emf 


  the pd across the cell when no current is flowing