The table below shows measurements made during a school investigation of dark adaptation. Each student sat in a dim room after leaving bright outdoor light....
Question 1 Report
The table below shows measurements made during a school investigation of dark adaptation. Each student sat in a dim room after leaving bright outdoor light. The light threshold is the lowest light intensity detected by the human eye.
| Time in dim room / min | Light threshold / arbitrary units |
|---|---|
| 0 | 80 |
| 5 | 42 |
| 10 | 23 |
| 15 | 14 |
| 20 | 11 |
Fig. 1 shows the location of two types of light receptor cells in the retina.
(a) Describe the change in light threshold during the first 15 minutes. [2]
(b) Use Table 1 to calculate the percentage decrease in threshold from 80 units at 0 minutes to 20 units at 11 minutes. [2]
(c) Explain why dark adaptation helps people move safely through a poorly lit building. [3]
(d) Name the receptor cells that are especially useful in dim light. [2]
Answer Details
(a) The light threshold decreases from \(80\) units at 0 minutes to \(14\) units after 15 minutes. A lower threshold means that dimmer light can be detected. [2]
(b) \[\text{decrease}=80-20=60\text{ units}\] \[\text{percentage decrease}=\frac{60}{80}\times100=75\%\] [2]
(c) Dark adaptation allows the eye to detect lower light intensities. Dim objects and obstacles become more visible, reducing the risk of trips, collisions and falls in a poorly lit building. [3]
(d) Rod cells are especially useful in dim light. They are receptor cells in the retina and are more sensitive to low light than cone cells. [2]
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