Circuit Devices

• What is the symbol for a light dependent resistor (LDR)?

  It is a specific electrical symbol
• How does the resistance of an LDR change in light conditions?

  Resistance is low in light and high in dark
• What is the relationship between current and potential difference in an ohmic conductor?

  Current is directly proportional to potential difference
• What happens to the current through a resistor when the temperature is constant?

  It remains directly proportional to potential difference
• What is the term used for a resistor that follows Ohm's law?

  Ohmic conductor
• What happens to the resistance of an LDR in dark conditions?

  Resistance is high in dark conditions
• How can LDRs be used in mobile phones?

  To detect when the phone is held to the ear
• How does an LDR function in a mobile phone circuit?

  • LDR in series with a lamp
  • Low resistance in light, high in dark
  • Potential difference shared between components
  • Lamp lights up when LDR resistance is low
  • Lamp dims when LDR resistance is high
• What is the potential difference across the LDR when it is in light?

  It is very low in light conditions
• What happens to the potential difference across the lamp when the LDR is in darkness?

  It becomes very low in darkness
• What is a common application of LDRs in garden lamps?

  They turn on in darkness and off in light
• What are the key characteristics of an LDR?

  • High resistance in dark
  • Low resistance in light
  • Used to detect light levels
  • Common in mobile phones and garden lamps
• Where can you find more questions about LDRs?

  In the vision workbook linked above
• What is the symbol for a thermistor?

  Thermistor symbol
• How does the resistance of a thermistor change with temperature?

  Resistance decreases as temperature increases
• In which devices are thermistors commonly used?

  Thermostats
• What are the characteristics of light dependent resistors (LDRs)?

  • High resistance in dark conditions
  • Low resistance in light conditions
  • Used in devices like garden lamps
• What happens to the resistance of a thermistor at low temperatures?

  Resistance is very high
• What occurs to the resistance of a thermistor at high temperatures?

  Resistance falls to a low level
• How do thermistors function in cooling systems for computers?

  They control fan operation based on temperature
• What happens to the potential difference across a thermistor when the temperature rises?

  Potential difference across thermistor decreases
• What is the effect of a high resistance thermistor on a fan's speed?

  Fan operates at low speed
• What happens to the potential difference across the fan when the thermistor's resistance decreases?

  Potential difference across fan increases
• How does a thermistor function in an incubator for premature babies?

  It detects temperature drops to activate alarms
• What are the applications of thermistors?

  • Used in thermostats
  • Control cooling fans in computers
  • Monitor temperatures in incubators
• Where can students find questions on the use of thermistors?

  In the vision workbook
• What is the main function of a thermostat?

  To turn appliances on or off based on temperature