Prisms
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-465
2025-12-18
27
If the surfaces of the transparent medium are not parallel, the emerging ray will not be parallel to the incident ray. When the cross section of the medium is a triangle, the medium is a prism. The path of a ray passing through a prism is shown in Fig. 1. When the ray from L strikes the prism at D, it is bent toward the normal and passes through the prism in the direction DH. When. it passes out of the prism at IH it is bent from the normal in the direction HK. A ray of light passing through a prism is always bent toward the base. If the eye is placed at K, the source of light will appear to be at L'. The position of any object seen through a prism is apparently moved toward the refracting angle, which is the angle formed by the intersection of the two faces under consideration.
If L is raised, the refracted ray DH is bent nearer, the base and the angle which it makes with the normal to the side AC is increased. When it reaches the value 42° the critical angle of the glass is reached and the ray is totally reflected within the glass and emerges from the prism through the side ВС.
The angle of deviation is the angle which the incident and emergent rays form with each other. In Fig. 1 it is the angle KNO. This angle varies with the refracting angle of the prism, the index of refraction of the medium, and the angle of incidence. There is for every prism a minimum angle of deviation, and this is obtained when the angles of incidence and emergence are equal.
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