The document discusses the properties and behavior of light, including reflection, refraction, and how different materials and optical components like lenses interact with light. It explains how lenses can refract light to form real or virtual images, and the factors that determine the type of image formed such as whether the object is between the focal point and lens or beyond it. Different lens shapes and cylindrical lenses are also described.

8. Reflection

12. Apex Angle of the prism

13. Refraction by a glass plate with non-parallel sides. The two sides AC and HF are not parallel. The beam is therefore bent from the position AB to DC on entering the plate, and from the direction EF to HG on leaving the plate. Its original direction is thus completely changed.

15. Example of use of prism

19. Fig. -- Refraction to a focus by convex lens (two prisms placed base to base) can bring two rays of light, originally parallel, to a focus.

20. Fig.The refraction of light by concave lens (two prisms placed apex to apex ) refract light in a diverging manner.

21. Fig. Refraction of light by a system of prisms. A system of prisms arranged apex to apex, as shown in the figure, refracts light in a diverging manner. Such a system constitutes a concave lens. P', P", P"' may be taken as the prism elements in the lens. Diverging effect is produced by a concave lens

23. Fig. The formation of convex lenses. A biconvex lens may be considered as formed by the intersection of two spheres whose centres are O" and O‘.

24. Fig. The formation of concave lenses. A biconcave lens may be considered to be formed by the approximation of two spheres whose centres are O" and O'.

25. Fig. The formation of concave lenses. A plano-concave lens, is formed by the approximation of a sphere and a plane surface.

27. Fig. The incident rays are parallel, coming from infinity; the focus (F) is called the principal focus. In practice, an object which is 6 metres or more away, is considered to be at infinity, and the rays of light issuing from it are parallel

28. Fig. The source of light (A) is between infinity and F; the focus is at a point, B, a corresponding distance on the other side of the lens. A and B are conjugate foci.

29. Fig. The source of light (A) is between F and the lens; the focus is at a point, B, behind the source of light. B is a virtual focus.

30. Fig. The image formed by a convex lens. The object (AB) is beyond the principal focus F1. The image (ab) is smaller, inverted, and also beyond the principal focus (F2) on the other side of the lens. In this case the image is real.

31. Fig. The image formed by a convex lens. The object (AB) is within the principal focus (F,). The image (ab) is larger, erect, and behind the principal focus on the same side of the lens. In this case the image is virtual.

36. Fig. The action of a convex cylinder. Rays of light striking the cylinder perpendicularly to the axis A'A" are brought to a focus in the focal line F'F".

37. Fig. Refraction of light by a concave cylinder. Rays of light striking the cylinder perpendicularly to the axis A'A" are diverged, and appear to be brought to a virtual focal line F'F"

41. Fig. Refraction by an astigmatic lens: Sturm's conoid . VV, the vertical meridian of the refracting body, is more curved than HH, the horizontal meridian. A, B, C, D, E, F, G show different sections of the beam after refraction. At B the vertical rays are brought to a focus: at F the horizontal rays are brought to a focus. From B to F is the focal interval of Sturm . D shows the circle of least diffusion .

44. Fig. The measurement of the strength of lenses. A straight line is viewed through the lens and the latter is moved in the direction of the arrow. In the case of a concave lens (A) the line appears to be displaced in the direction of movement. In a convex lens (B) the line appears to be displaced in the opposite direction.

46. Fig. Refraction by a system of lenses.

47. Fig. Refraction by a system of lenses. If the system consists of two lenses, A and B, separated by a distance G, the image after refraction by the first lens would be formed at a, but on meeting B, the rays are further converged (or diverged), and brought to a final focus at F.

48. Fig. The cardinal points of a compound homocentric system. AB, the object; ab, the image; Bb, the line upon which the system is centred; F and F" are the two principal foci; H' and H", the two principal points; N' and N" the two nodal points; PR and QS are the two principal planes.

49. Fig.The equivalence and vertex power of a thick lens in air. The first nodal point and the first principal points coincide; similarly the second.

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