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The Propagation of Light

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-436

2025-12-24

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The Propagation of Light . A luminous ray is a single line of light propagated from a luminous point. It is always perpendicular to the front of the advancing light wave, and in the case of a spherical wave is a radius drawn from the source of light. A group of rays from the same source is a pencil of rays. If these rays are parallel, they constitute a beam of light. If they diverge from a point, they form a diverging pencil. If they meet at a point, they form a converging pencil.

In a homogeneous medium, the direction of propagation of light is in straight lines. But light is affected by gravitation; thus, when the ray from a star passes near the sun it is bent slightly towards the sun out of its straight-line path, to the extent predicted by Einstein.