Circuits Flashcards
What is an LDR?
A light dependant resistor. The intensity of its resistance depends on the intensity of light. In the darkness the resistance is highest.
What kind of applications do LDR’s have?
.automatic night lights
. outdoor lighting
. burglar detectors
What is a thermistor?
A temperature dependant resistor. In hot conditions the resistance drops and in cool conditions it goes up.
What applications do thermistors have?
. car engine temp sensors
. electronic thermostats
What are sensing circuits used to do?
To turn on/increase power to components depending on the conditions they’re in.
How will the sensing circuit be set out?
There will be one fixed resistor and another resistor (potentially a thermistor or LDR) and there’ll be a component that’s in parallel with one of the resistors.
What can be said of the resistor and component that are connected in parallel?
They will always have the same pd coz they’re connected in parallel.
How is the pd of the power supply shared out?
The pd of the power supply is shared out between the resistor and the loop made of the other resistor and component according to their resistances. - the bigger a components resistance, the more of the pd it takes
How would an increase in temp affect the distribution of pd if one of the resistors is a thermistor?
The resistance of the thermistor would decrease and therefore , the pd at the thermistor would also decrease (it takes a smaller share) so the pd across the fixed resistor would increase and if the fixed resistor is in parallel with a component, there’ll be more energy transferred to the component.
What if the component is parallel to the variable resistor (e.g. a bulb and an LDR)?
The pd across both the bulb and LDR will be high when it’s dark and the LDR’s resistance is high. The greater the pd across a component the more energy it gets so a bulb connected to an LDR would get brighter as the room got darker.
