Physics · Oct / Nov 2023 · Paper 62 · Question 4
0625
As printed in the paper
The question as text
A student investigates the effect of changing the colour of light on the focal length of a lens. The focal length f of a lens is given by the equation f = uv (u + v). The distance u is the distance between an object and the lens. The distance v is the distance between the lens and the image that is formed on a screen. Plan an experiment to investigate the effect of changing the colour of light on the focal length of a lens. The following apparatus is available to the student: • illuminated object • a selection of coloured filters to change the colour of the light • converging lens • screen • metre ruler. Other apparatus normally available in a school laboratory can also be used. In your plan, you should: • draw a labelled diagram to show the arrangement of the apparatus • explain briefly how you would do the investigation, including the measurements you would take • draw a suitable table, with column headings, to show how you would display your readings (y not required to enter any readings in the table) • state how you would use your results to reach a conclusion.
Read automatically from the paper; the printed page above is exact.
Show the answer and mark scheme
MP1
labelled diagram
diagram with lens between object and screen, and filter anywhere between the illuminated object and the lens or between the source of illumination and the object, with a least 1 label
MP2
method
move object / lens / screen to obtain focused / sharp / clear image
MP3
measure / record / find / calculate / note u and v
MP4
calculate / determine / find the focal length
MP5
repeat with different colours / filters
MP6
table
table with clear columns for (filter) colour, u and v
AND with appropriate units
MP7
how to reach conclusion
plot bar chart of focal length and colour OR
compare results to see if / how the change of colour affects the focal length OR
compare results to determine the effect of a change in colour on the focal length
Additional graph notes:
NOTE: – The principle to apply here is ‘could I draw a significantly better line, using these points, under examination conditions?’ If the answer is definitely ‘yes’, do not award the mark.
NOTE: –
If candidate’s scale consists of actual readings at equal intervals this will produce a perfect straight line! The only marks available in this case are the first (axes right way round and labelled) So maximum 1.
If axes are wrong way round, the other 3 marks are still available.
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