1. A –Level Physics: Electrical Quantities: Semiconductors

2. Objectives: Additional skills gained: Undertaking practical work
47. understand how changes of resistance with temperature may be modelled in terms of lattice vibrations and number of conduction electrons and understand how to apply this model to metallic conductors and negative temperature coefficient thermistors
48. understand how changes of resistance with illumination may be modelled in terms of the number of conduction electrons and understand how to apply this model to LDRs.
Additional skills gained:
Undertaking practical work
Developing planning skills

3. Starter: Recap
If EMF= 12V and a variable resistor is set up with the contact positioned 7cm along the 15cm length. Calculate the potential difference along this 7cm.
Explain an experiment that would allow you could calculate the resistivity of a wire (you’ve done this experiment before!)
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4. Draw a V-I graph for this component
Effect of Temperature: Filament
As the potential difference across a filament bulb increases, the temperature of the wire gradually increases (more energy supplied)
As such, the metal ion lattice will vibrate with higher amplitude, increasing the likelihood of collisions thus increasing the resistance of the wire.
Draw a V-I graph for this component
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5. Semiconductors
Semiconductors are components that have a high resistance due to a low density of charge carriers.
When heated or exposed to light (component dependent), the density of charge carriers increases, reducing the resistance!
Draw the symbols for a) an LDR b) a thermistor c) a diode and also draw resistance graphs for a) and b)
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6. Experiment: Investigate resistance
Experiment 1: LDR
Connect a multimeter to an LDR (set to ohms)
Take measurements in 1) darkness 2) exposure to room light 3) exposure to intense light
Experiment 1: Thermistor
Connect a multimeter to a thermistor (set to ohms)
Take measurements in 0C, 20C, 40C, 60C, 100C

7. Complete revision sheet (A3 booklet) number 4 by Friday
Independent Study
Complete revision sheet (A3 booklet) number 4 by Friday