1. Be able to describe how the resistance of LDRs and Thermistors varies.
08 November 2018
LDRs and Thermistors I
Objectives
Be able to describe how the resistance of LDRs and Thermistors varies.
HSW: AF4 – Using investigative approaches
Used before in: lesson 7 - Diodes
Will use again in:
PLTS: Team workers – Work collaboratively with others.
Keywords
Current (I), Amp, Voltage (V), Volts, ammeter, voltmeter, resistor, thermistor, LDR, resistance (R), Ohm.
Draw the symbols – which is which?
LDR
Thermistor

2. OUTCOMES
All students should be able to describe that not all components conduct electricity by Ohm’s Law.
Most students should be able to describe the shape of Resistance-Light Intensity Graph for an LDR and Resistance-Temperature Graph for a Thermistor.
Some students should be able to explain that semiconductor components use energy to release electrons and that this reduces resistance.

3. Student Model thermistors and LDRs
What happens to atoms when the amount of energy increases?
What happens to electrons as the amount of energy increases?
What happens to the resistance as the amount of energy increases?

4. Current-Potential Graph of a filament bulb
Set up the equipment as shown:
Follow the instructions on the sheet and take readings of resistance.
Analysis
Once you have a set of results draw a graph of Resistance on the y-axis and your independent variable on the x-axis and write a conclusion.
Results
Independent variable (temperature or Light intensity)
Resistance (Ω)

5. Two simple components:
1) Light dependant resistor – resistance DECREASES when light intensity INCREASES
2) Thermistor – resistance DECREASES when temperature INCREASES
Resistance
Amount of light
Resistance
Temperature
08/11/2018

6. Electrical Taboo
Can you describe all the circuit symbols without saying the words on the cards?