Laboratory work: determining the optical power of a lens
The aim is to measure F and D of a converging lens. Place the lamp (object), the lens and the screen in a line at one height. Only the teacher switches the lamp on and off; its glass gets hot, so do not touch it or its wires. With the lens at a distance d₁ from the lamp, move the screen to find where a sharp image of the filament forms, and measure f₁ from lens to screen. Repeat at d₂ and d₃. For each pair calculate F = df/(d + f), then F_mean = (F₁ + F₂ + F₃)/3 and D = 1/F_mean. Then try the cases d = 2F, F < d < 2F and d < F and watch the type of image: for d < F there is no image on the screen because it is virtual.
Make a table: experiment no., d, f, F, F_mean, D. Compare the image size at d = 2F and F < d < 2F: when is it larger? Analyse the results and list the sources of error (uncertainty in finding the sharp image, measuring the distances).