Gilbert light experiments for boys . therefore BR and BP divergeafter they pass through the lens and do not form an image. Youreye, however, makes an image because it sees the rays as thoughthey came from MI. This explains why you see anything insidethe focal length as enlarged and right side up. In (3), BO is outside the virtual focus of the diverging and BP diverge after they pass through the lens and youreye sees the image MI. This explains why diverging lensesalways give images small and right side up. POWER OF A LENS Spectacles are lenses, and opticians measure the power of thespe
Gilbert light experiments for boys . therefore BR and BP divergeafter they pass through the lens and do not form an image. Youreye, however, makes an image because it sees the rays as thoughthey came from MI. This explains why you see anything insidethe focal length as enlarged and right side up. In (3), BO is outside the virtual focus of the diverging and BP diverge after they pass through the lens and youreye sees the image MI. This explains why diverging lensesalways give images small and right side up. POWER OF A LENS Spectacles are lenses, and opticians measure the power of thespectacle lenses as follows: If the lens has a focal length of1 meter it is said to have a power of 1 diopter; if it has a focallength of 1-2, 1-3, or 1-10 meter it is said to have a power of 2, 3,or 10 diopters; and so on. That is, the shorter the focal lengththe greater the power. GILBERT LIGHT EXPERIMENTS 111 A meter is 100 centimeters long. You will find on most or-dinary rulers 30 divisions on the side opposite the inch divisions;. Fig. 169. Conjugate foci each of these divisions is 1 centimeter, and 100 of these makea meter. Experiment No. 109. Power of your lenses. Measure incentimeters the focal length of the 8-inch lens. Do you find 100 it to be 20 cms. ? Is the power of the lens then = 5 diopters ? 20 Repeat with the 4-inch lens. Is its focal length 10 cms. and100 its power == 10 diopters ? 10 Experiment No. 110. Power of spectacles. Measure in centi-meters the focal length of your fathers or mothers spectaclesand calculate their power in diopters. Experiment No. 111. Conjugate foci. Get the image of acandle as in Fig. 169, mark the position of the screen and thecandle, and then exchange them. Do you again find an image,but of different size? Repeat at different distances. Two points so situated with respect to a converging lens thatan object at either forms an image at the other are called conjugatefoci. There are an infinite number of pairs of such points foreach conve
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