A text-book of physics, largely experimentalOn the Harvard college "Descriptive list of elementary physical experiments." . imenter must take care notto let any idea he may have as to the position where an image-pointought to be affect his judgment in deciding where it is. After all the five image-points are found, connect them, No. 1 toNo. 2, No. 2 to No. 3, etc., by means of straight lines, thus gettinga rough representation of the whole image. Draw from each object-point toward the corresponding image-point a straight line as long as the ruler (No. 23), and note the pointwhere these lines c
A text-book of physics, largely experimentalOn the Harvard college "Descriptive list of elementary physical experiments." . imenter must take care notto let any idea he may have as to the position where an image-pointought to be affect his judgment in deciding where it is. After all the five image-points are found, connect them, No. 1 toNo. 2, No. 2 to No. 3, etc., by means of straight lines, thus gettinga rough representation of the whole image. Draw from each object-point toward the corresponding image-point a straight line as long as the ruler (No. 23), and note the pointwhere these lines cross each other. 165. Formation of the Image in Exercise 28.—The for-mation of the image-points in Exercise 28 is illustrated byFig. 139. One ray from the object-point A follows asecondary axis (§ 160) passing through the centre of thelens, and its direction after leaving the lens is the same asbefore entering it. (Its direction inside the lens is notquite the same, but the figure does not show this.) Another ray from A runs parallel to the principal axis(§ 160) before entering the lens, and will therefore pass ,1. B FIG. 139. through the principal focus, /, on the farther side of thelens. The crossing of these two rays at A shows the posi-tion of the image of A. In a similar way B, the image of B, is located. 166. Size and Shape of Image.—If a straight line isdrawn from A to B in Fig. 139, we may call this thelength of the image, although the images of points betweenA and B will not lie on this line. It is evident from ; and also from the figure obtained in Exercise 28, that 194 PHYSICS. the distance A^B is to the distance AB as the distance ofABf from the lens is to the distance of AB from the lens. The curved shape of the image obtained in Exercise28, if the work has been correctly done, is due partly to thefact that the ends of the object-arrow are farther from thelens than the centre of the arrow, and partly to the factthat the focal length along a secondary a
Size: 2880px × 868px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectphysics