A student conducts an experiment to determine the focal length of a thin converging lens. The table below shows two sets of measurements of the object distance UUU, the image distance VVV, and the total distance DDD:
TrialU/cmV/cmD/cm124.036.060.0222.040.062.5 \begin{array}{|c|c|c|c|} \hline \text{Trial} & U / \text{cm} & V / \text{cm} & D / \text{cm} \\ \hline 1 & 24.0 & 36.0 & 60.0 \\ \hline 2 & 22.0 & 40.0 & 62.5 \\ \hline \end{array} Trial12U/cm24.022.0V/cm36.040.0D/cm60.062.5Use the results from the first trial to calculate a value f1 f_1\,f1 for the focal length of the lens. Use the equation f1=UVD\displaystyle f_1 = \frac{UV}{D}f1=DUV.
Use the results from the second trial to calculate a value f2 f_2\,f2 for the focal length of the lens. Use the equation f2=UVD\displaystyle f_2 = \frac{UV}{D}f2=DUV.
Calculate the average value favgf_{\text{avg}}favg for the focal length of the lens. Give your answer to a suitable number of significant figures for this experiment.
Suggest two practical reasons why it may be difficult to obtain highly reliable results in this lens experiment.
A student states that a more reliable value for the focal length is obtained if more values of UUU, VVV, and D D\,D are collected, enabling a graph of UV UV\,UV against D D\,D to be plotted.
Suggest a suitable number of values for UUU.
Suggest a suitable range of values for UUU.
56 exam-style questions on CIE IGCSE Physics 3.2.3a Converging and diverging lenses. Each one has a worked solution and a mark scheme showing where the marks go.