A student used a lamp to change the light intensity reaching some pondweed. The light intensity reaching the pondweed is inversely proportional to the square of the distance between the lamp and the pondweed.
light intensity in arbitrary units = 1÷d2 1 \div d^2\,1÷d2
In this equation d is the distance between the lamp and the pondweed in metres.
The lamp was placed 0.20 m from the pondweed. Calculate the light intensity reaching the pondweed.
The student then moved the lamp to 0.50 m from the pondweed. Calculate how many times smaller the light intensity reaching the pondweed is at 0.50 m than at 0.20 m.
The student expected the number of bubbles released each minute at 0.50 m to be 6.25 times smaller than at 0.20 m. It was only 3 times smaller.
Suggest one reason why.
54 exam-style questions on AQA GCSE Biology 4.1 Photosynthesis, covering 4.1.1 Photosynthetic reaction, 4.1.2 Rate of photosynthesis, and 4.1.3 Uses of glucose from photosynthesis. Each one has a worked solution and a mark scheme showing where the marks go.