light dependent resistors

• Light dependent resistor (LDR)


  Also called a light dependent resistor
• LDR

  • High resistance in dark conditions
  • Low resistance in light conditions
• How LDRs work in circuits

  1. LDR has high resistance in dark

  2. LDR has low resistance in light

  3. Low resistance allows current to pass easily

  4. High resistance limits current flow
• Devices using LDRs

  • Mobile phone screen backlight
  • Garden lamps
• Phone held to ear

  LDR in darkness, resistance rises sharply
• LDR resistance rises sharply

  Potential difference across LDR increases, less energy for lamp
• Less energy for lamp

  Lamp becomes dim, screen turns off
• Mobile phone circuit is more complicated than the example shown
• The example circuit uses a 10V cell