Light: An Elementary Text-book, Theoretical and Practical for Colleges and Schools |
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adjusted angle of incidence appear axis beam blue candle coincide colour concave lens concave mirror converge convex lens cornea critical angle crown glass crystalline lens deviation direction distant object distinct vision Draw emergent rays equal experiments eyepiece focal length formed by reflexion formula front gas flame green Hence illuminating power image formed inches incident ray inverted lenses light falls light travels long-sighted looking luminous magnifying power measured medium microscope millimetre moved nearer normal object glass object PQ obliquely observer paper path pencil of rays perpendicular placed plane mirror plate principal focus prism produced pure spectrum radius rays diverging real image reflected rays refractive index retina screen Section seen shew shewn in fig slit source of light spherical surface telescope traverse tube velocity of light vertical violet virtual image white light yellow
Popular passages
Page 54 - When a ray of light passes from one medium to another, it is refracted so that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the velocities in the two media.
Page 163 - Fig. 112. object glass equal to its focal' length. But before reaching p they are intercepted by the concave lens bac, which forms the eyepiece, placed in such a position that aq is its focal length. The rays therefore emerge from the lens as a parallel pencil parallel to ap and capable of producing normal vision in an eye placed to receive them. The image seen is magnified and erect. This arrangement of lenses is used in opera and field glasses, which consist of two such telescopes, one for each...
Page 15 - I'/a'*. Thus, when these two intensities are equal, we have T=&" Hence the illuminating powers of two lights are proportional to the squares of the distances at which they produce equal intensities of illumination respectively. 12. Candle Power. It is necessary of course to have some standard of illuminating power, in terms of which the illuminating powers of other lights may be expressed. The standard ordinarily in use, though it is by no means a satisfactory one, is the illuminating power of the...
Page 157 - Hence the magnification, as thus defined, is measured as before by the ratio of the size of the image to that of the object, when the image is at the least distance of distinct vision.
Page 53 - REFLEXION. (1) The incident ray, the normal to the surface at the point of incidence, and the reflected ray lie in one plane. (2) The angle between the reflected ray and the normal is equal to that between the incident ray and the normal.
Page 108 - Would the image be real or virtual ? 9. A bright object, 4 inches high, is placed on the principal axis of a concave spherical mirror, at a distance of 15 inches from the mirror. Determine the position and size of its image, the focal length of the mirror being 6 inches. 10. Describe an experiment to verify the laws of reflexion of light...
Page 20 - It has been found by experiment that the illumination of an object varies inversely as the square of its distance from the source of light.