1. Electrical Circuits 8
3.1 j Explain the design and use of circuits to explore variation of resistance – including for lamps, diodes ntc thermistors and LDR’s

2. Starter What is the component? What is function of the component?
How does current change with voltage?
How does the resistance of the component change? Why?

3. We are going to investigate the resistance in aLDR and a thermisitor?
LDRs (light-dependent resistors) are used to detect light levels, for example, in automatic security lights. Their resistance decreases as the light intensity increases.
Thermistor - are used as temperature sensors, for example, in fire alarms. In the most common type of thermistor, the resistance decreases as the temperature increases

4. LDR investigation
You will carry out an investigation to measure the resistance of an LDR at different light intensities.
An LDR is an electric component whose resistance varies with light intensity.
Method:
Connect the LDR to a multimeter and set it to 20kΩ,
Place a desk lamp so that the bulb is 10cm away from the LDR and record the resistance
Vary the desk lamp distance and measure the resistance accordingly.
Light intensity can be expressed as an ordered variable: bright, medium and dim.
Plot a graph of resistance against light intensity.

5. Thermistor investigation
You will carry out an investigation to measure the resistance of a thermistor at different temperatures.
A thermistor is an electric component whose resistance varies with temperature.
Method:
Heat 250ml of water using a bunsen burner to 80ºC then turn the bunsen burner off,
Immerse the thermistor in the hot water,
Connect the thermistor to a multimeter and set it to 20kΩ,
Record the temperature of the water as it cools down
Record the resistance of the thermistor for each corresponding temperature
Plot a graph of resistance against temperature.

6. Thermistors and LDRs can work as Sensors: A sensor is a component that allows a physical quantity to change its resistance and hence control the amount of current flowing in a circuit. A A
Light Dependent Resistor/ LDR: Its resistance decreases as the light intensity increases. (The higher the illumination, the higher the current
Temperature Dependent Resistor /Thermistor: Its resistance decreases as the temperature increases. (The higher the temperature, the higher the current).
In this circuit, the LDR can work as a lightmeter. The higher the ammeter reading, the higher the illumination.
In this circuit, the thermistor can work as a thermometer. The higher the ammeter reading, the higher the temperature.

7. Results Plot graph – Write conclusion using key language.
Light intensity / temperature on the x axis
Resitance on the y axis
Write conclusion using key language.
Resistance Light intenisty Temperature Thermistor
LDR increase decrease

8. Plenary
Pair/ share
Explain the shape of graph and conclusion to another a person who investigated the other component.
Class
You will explain their conclusion to the class.