Page 09 14. A student carries out an experiment to investigate how irradiance varies with distance. A small lamp is placed at a distance d away from a light meter. The irradiance I at this distance is displayed on the meter. This measurement is repeated for a range of different distances. The student uses these results to produce the graph shown. I 0 2 1 d The graph indicates that there is a systematic uncertainty in this experiment. Which of the following would be most likely to reduce the systematic uncertainty in this experiment? A Repeating the readings and calculating mean values. B Replacing the small lamp with a larger lamp. C Decreasing the brightness of the lamp. D Repeating the experiment in a darkened room. E Increasing the range of distances. 15. A point source of light is 8·00 m away from a surface. The irradiance, due to the point source, at the surface is 50·0 mW m−2. The point source is now moved to a distance of 12·0 m from the surface. The irradiance, due to the point source, at the surface is now A 22·2 mW m−2 B 26·0 mW m−2 C 33·3 mW m−2 D 75·0 mW m−2 E 267 mW m−2. [Turn over