Heat and Light: An Elementary Text-book Theoretical and PracticalUniversity Press, 1894 - 434 σελίδες |
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adjusted angle of incidence appear axis beam blue candle coincide colour concave lens concave mirror converge convex lens convex mirror 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
Δημοφιλή αποσπάσματα
Σελίδα 53 - 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.
Σελίδα 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.
Σελίδα 163 - Fig. 112. from the 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...
Σελίδα 15 - 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 standard candle. Standard candles are sperm candles, six to the pound, burning at the rate of 120 grains per hour.
Σελίδα 108 - How far from a concave mirror of radius 3 feet, would you place an object to give an image magnified three times ? Would the image be real or virtual ? 9.
Σελίδα 138 - What is its true distance ? (/t = l-5.) 23. A convergent pencil of light falls upon a concave lens. Trace the position of the image as the point of convergence of the pencil moves from an infinite distance up to the lens. 24. What is meant by the statement — the focal length of a given convex lens is 2 feet ? Draw a figure, approximately to scale, indicating the paths of the rays of light and the positions of the images formed, when...
Σελίδα 36 - L' is a virtual image of L. Moreover it will be found from the figure by direct measurement that LL' is perpendicular to the mirror and that L'A is equal to LA. Thus the image of a point formed by a plane mirror is virtual and its position is obtained by drawing a normal from the point to the mirror, and producing it as far behind the mirror as the point is in front of it. This result may be verified in the following way. EXPERIMENT (7). To verify the position of the image of a point formed by a...
Σελίδα 14 - The intensity of the illumination at a point due to a given source is inversely proportional to the square of the distance of the point from the source.
Σελίδα 30 - The laws of refraction may be stated in a form resembling that adopted for the laws of reflexion. (1) The incident ray, the normal to the surface at the point of incidence, and the refracted ray lie in one plane. (2) The...