Light-Dependent Resistors

• How does the resistance of an LDR change in light conditions?

  Resistance is low in light and high in dark
• What is the function of an LDR in circuits?

  To detect light and change resistance
• What is the potential difference across a resistor when current is measured?

  It gives a straight line passing through zero
• What type of conductor is a resistor when temperature is constant?

  It is called an ohmic conductor
• What happens to the resistance of an LDR in dark conditions?

  It has a high resistance
• What happens to the resistance of an LDR in light conditions?

  It has a low resistance
• How does an LDR function in a mobile phone?

  It detects when the phone is near the ear
• How is an LDR used in a mobile phone circuit?

  • LDR in series with a lamp
  • Cell provides 10 volts potential difference
  • Low resistance in light allows lamp to light up
  • High resistance in dark dims lamp, turning screen off
• What happens to the potential difference across the LDR when it is in darkness?

  It becomes very high
• What happens to the potential difference across the lamp when the LDR is in darkness?

  It becomes very low
• How do garden lamps utilize LDRs?

  • Light turns on in darkness
  • Light turns off in daylight
  • Automatically responds to ambient light conditions
• What is the relationship between light intensity and LDR resistance?

  High light intensity means low resistance
• How does the potential difference across components in series behave?

  It is shared among the components