Circuit Devices Flashcards
What is LDR?
a resistor that is dependent on the intensity on light
LURD
DARK = RESISTANCE IS THE HIGHEST
They have lots of appliances including automatic night lights, outdoor lighting and burglar detectors
What is a thermistor ?
A temperature dependent resistor.
TURD
cool conditions = resistance up
Thermistor make useful temperature, e.g. car engine temperature sensors and electronic thermostats
How can sensing circuit be used ?
used to turn on or increase the power to components depending on the condition they are in.
2) page 182
3) the fixed resistor and fan will always have same pd across them ( fr and thermistor in same line while fan is in parallel to fr)
4) the pd of the power suppy is shared out between the thermistor and the loop made up of the fixed resistor and the fan according to their resistances - the bigger a components resistance, the more of the pd it takes
What occurs as the room gets hotter ?
the resistance of thermistor decreases and it takes a smaller share of the pd from the power supply so the pd across the fixed resistor and fan rises, making the fan go faster.
You can also connect the component across the variable resistor instead
For example:
connect bulb in parallel to LDR, the pd across both the LDR and the bulb will be high when it’s dark and the LDRs resistance is high. The greater the pd across a component, the more energy it gets. So a bulb connected across an LDR would get brighter as the room gets darker.
