Current and potential difference

• switch symbol

  switch

  
• lamp symbol

  lamp

  
• fuse symbol

  fuse

  
• cell symbol

  cell

  
• voltmeter symbol

  voltmeter

  
• diode symbol

  diode

  
• thermistor symbol

  thermistor

  
• resistor symbol

  resistor

  
• variable resistor symbol

  variable resistor

  
• LDR symbol (light dependent resistor)


  LDR

  
• LED symbol (light emitting diode)

  LED

  
• what does a circuit need for an electrical charge to flow through it

  a source of potential difference
• the size of the electric current is

  the rate of flow of electric charge
• what is charge flow measured in

  coulombs C
• what is current measured in

  amps A
• how does the current differ within a single closed loop

  a current has the same value at any point in a single closed loop
• how does resistance effect current of a component

  the greater the resistance of the component the smaller the current for a given potential difference across the component
• describe a filament bulb graph

  the resistance of filament lamp increases as temperature increases

  
• describe a diode graph

  the current through a diode flows in one direction only , so it has a higher resistance in a reverse direction

  
• describe a resistor at constant temperature graph


  if resistance is constant, current is directly proportional to potential difference

  
• how does resistance change with current

  as current increases , electrons have more energy - electrons flow through resistor, collide with atoms in it - transfers energy to the atoms , they vibrate more - more difficult for electrons to flow through resistor - current decreases
• how does increasing resistance affect current

  as resistance increases , current decreases
• how does resistance change with temperature in normal wires

  electrons have more energy - collide with atoms in resistor - transfers energy to the atoms - vibrate more - harder for them to flow through resistor
• how does resistance change with temperature in a thermistor

  hotter temperature - lower resistance , used in temperature detectors/thermostats
• how does resistance change with length

  greater length - higher resistance - lower current , electrons have to make there way through more resistor atoms - harder than using short wire
• how does resistance change with light

  greater light intensity - lower resistance , resistance is greater when dark - used in automatic night lights
• how does resistance change with voltage

  diode allows current to flow in one direction , in opposite direction , has high resistance so no current can flow