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Total Reflection: Critical Angle

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-460

2025-12-18

557

Demonstration. - Fix on the optical disk a semicircular piece of plate glass, as in Fig. 1. Rotate the shield and allow a single narrow band of light to strike on the cylindrical surface at various angles to the horizontal. At some angles the beam on reaching the plane side of the glass will be reflected back into the glass and pass out at the upper surface. At other angles part of the beam will pass through the glass, undergoing refraction as it leaves the plane surface. At a certain angle of incidence, the refracted beam will just graze the plane surface of the glass.

This angle of incidence, where total reflection begins, is called the critical angle, and varies with the media. The critical angle for light passing from water into air is about 48.5°; from crown glass into air, 42°; and from diamond into air, 24°.