A student investigates how the resistance of a light-dependent resistor (LDR) changes with distance from a light source.
Which of these is the correct circuit symbol for an LDR?
The student sets up a desk lamp on a meter ruler and places the LDR at various distances from the lamp inside a completely darkened room.
Explain why the student must conduct the investigation in a completely darkened room.
To determine the resistance of the LDR, the student also uses a voltmeter and an ammeter. State how the voltmeter and the ammeter should be connected relative to the LDR.
The table below shows the student's results.
| Distance (cm\text{cm}cm) | Resistance (Ω\OmegaΩ) |
|---|---|
| 10 | 200 |
| 20 | 500 |
| 30 | 900 |
| 40 | 2100 |
| 50 | 1950 |
| 60 | 2600 |
| 70 | 3300 |
Identify the anomalous reading in the table, giving its distance and resistance.
State the expected range of resistance at this distance if it followed the trend shown by the other data points.
Why is it difficult to obtain reliable resistance readings very close to the lamp (e.g., less than 5 cm)?
Suggest one way the student could vary the light intensity reaching the LDR without moving the lamp.