(i) The candle is placed at a distance, u from the lens and the screen position adjusted until a sharp image is obtained. The image distance, v between lens and screen is measured. The process is repeated for other values of u and v; for each set of u and v, focal length, f is found using the formula: $\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$. The average of the f value is the required focal length of the lens.
(ii) Diverging lens form virtual images that cannot be formed on the screen.
johnmulu answered the question on May 29, 2017 at 08:56
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