# Physics - Thermistors and LDRs

> Source: https://ollybritton.com/notes/a-level/physics/topics/thermistors-and-ldrs/ · Updated: 2024-08-25 · Tags: physics, electricity, year-1, school

### Thermistors and LDRs as semiconductors
##### What type of conductor are thermistors??
Semiconductors.
^thermistor-is-semiconductor

##### What type of conductor are LDRs??
Semiconductors.
^ldr-is-semiconductor

##### How do thermistors and LDRs work??
They have a number density that changes in response to environmental effects.
^thermistor-ldr-number-density-mechanism

### Thermistor resistance behaviour
##### What does the resistance-temperature graph look like for a typical thermistor??
![paste-1027fd1cb7cd279c8cc1e5cfbfe9455775357f6f.jpg](https://ollybritton.com/assets/attachments/img/paste-1027fd1cb7cd279c8cc1e5cfbfe9455775357f6f.jpg)
^thermistor-resistance-temperature-graph

##### For a typical thermistor, what does a low temperature mean??
A high resistance.
^thermistor-low-temp-high-resistance

### Temperature coefficients
##### What does NTC stand for??
Negative Temperature Coefficient.
^ntc-stands-for

##### What does a Negative Temperature Coefficient mean??
* A low temperature will have a high resistance.
* A high temperature will have a low resistance.
^negative-temperature-coefficient-meaning

##### What does a Positive Temperature Coefficient mean??
* A low temperature will have a low resistance.
* A high temperature will have a high resistance.
^positive-temperature-coefficient-meaning

##### ![paste-f3f371ec5bc553fe206929caf5ce29137e46ae84.jpg](https://ollybritton.com/assets/attachments/img/paste-f3f371ec5bc553fe206929caf5ce29137e46ae84.jpg) Does this thermistor have a PTC or a NTC??
PTC
^identify-ptc-from-graph

##### ![paste-c13b7edce97422bd447dbbac279c63635074d0ab.jpg](https://ollybritton.com/assets/attachments/img/paste-c13b7edce97422bd447dbbac279c63635074d0ab.jpg) Does this thermistor have a PTC or a NTC??
NTC
^identify-ntc-from-graph

### LDR behaviour and comparison
##### What does the light intensity vs resistance graph look like for a typical LDR??
![paste-e0ecd5a3507eac59a0a2bcb5ee1c1eadd19a8bfd.jpg](https://ollybritton.com/assets/attachments/img/paste-e0ecd5a3507eac59a0a2bcb5ee1c1eadd19a8bfd.jpg)
^ldr-light-intensity-resistance-graph

##### What other component do LDRs and thermistors have the opposite IV characteristic to??
Filament Bulbs.
^opposite-iv-to-filament-bulb

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