4-ELC-04

Outcomes

• Pupils can explain how light intensity affects resistance in an LDR
• Pupils can explain how temperature affects resistance in a thermistor
• Pupils can set up data logging experiments and can take useful data

Specification References

• 2.13 describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature

Starter

No time for starters today folks, unless you count collecting laptops as a starter

Main Body of Lesson

The idea of the lesson is to investigate thermistors and LDRs. The twist is to use PASCO instead of traditional methods. To investigate the LDR blackout the room and use the light sensor and I-V sensor. Vary the distance of the lamp from the LDR and record the current and voltage every 10cm or so. You may need to switch the setting on the sensor to the middle one, if the brightness is too high then you'll need to switch to the lower sensitivity. It's probably easier to nake a note of the values and either put them in their books or excel than use datastudio for graphs etc.

To investigate the thermistor unblackout the room (H&S) and set up a bunsen, beaker of water etc. as far away from the laptop as possible. Also use a clampstand to hold the temperature probe. Have the pupils record current and voltage every 5K or 10K (depending on time). Plot graphs etc.

Should you wish to avoid the PASCO-fiasco then there are alternatives. However, PLEASE ENSURE THAT YOU MAKE IT CLEAR TO ED WHICH VERSION YOU WANT.

LDR testing can be achieved with blackout tubes and lamps on metre sticks, ammeters and voltmeters too.

Thermistor testing can be achived in a similar way to above but with thermometers, ammeters and voltmeters.

Plenary

If any pupils produce good graphs, have them email you their graphs and display them on the white board. I've included some results from my group in the folder.

Once pupils have produced graphs give them ideal results for their notes. A nice way to remember the results is as follows:

When it's cold and dark outside, your resistance to getting out of bed/the house is high

When it's hot and bright, your resistance to getting out of bed/the house is low

Additional Information

Resources Required

PASCO lesson

6 x the following

• PASCO hub
• Light sensor
• I-V sensor
• Temperature sensor (probe and hub connector)
• Lamp
• Thermistor
• LDR

Non-PASCO lesson

12 x the following

• simple ammeter
• simple voltmeter
• thermistor
• LDR (on a stick in a tube)
• Bulb (on a stick)
• thermometer

Safety/Hazards

• Water + Electricy = bad
• Water + laptop = expensive
• Lamps + people = burns
• Standard Bunsen procedures apply