1.1 - Electrical Circuits

• • Cell


  
• • Battery


  
• • Resistor


  
• • voltmeter 


  
• • ammeter 


  
• • switch


  
• • bulb/lamp


  
• Fuse

  
• LDR

  
• Thermistor

  
• variable resistor

  
• Diode

  
• LED

  
• a.c. power supply

  
• d.c. power supply

  
• variable d.c. power supply

  
• What can be said about the value of current at any point in a series circuit?

  • current is the same at all points in a closed loop
• What two factors does the current in a circuit depend on?

  • potential difference / voltage
  • resistance
• An ohmic conductor is a conductor for which current and voltage are directly proportional, the resistance remains constant as resistance changes and the temperature must be constant
• Four Components for which resistance is not constant as current changes?

  • Lamps
  • Diodes
  • LDRS
  • Thermistors
• What happens to the resistance of a filament lamp as the temperature increases?

  • resistance increases
  • ions in metal have more energy so they vibrate more causing collisions with electrons as they flow through the metal creating a greater resistance to current flow
• What is special about the current flow through a diode?

  • current flows in 1 direction
  • resistance is very high in the other direction preventing current flow
• the resistance of a thermistor will decrease as temperature increases
• 2 examples of when a thermistor may be used

  • in a thermostat to turn a heater on below a certain temperature
  • in a freezer to turn on a cooler when the temperature becomes too high
• As the light intensity decreases, the LDRS resistance increases
• LDRS are used in street lamps or night lights, when light levels become too low the light gains sufficient current to turn on
• Series - total voltage is shared between each component

  Parallel - voltage is the same all across
• If two resistors are connected in parallel, their total resistance is less than the smaller of the 2 individual resistances
• if two resistors are connected in seres, their total resistance us equal to the sum of 2 individual resistances
• The current through a diode only flows in onedirection.