Basic Laws of Geometrical Optics: Experimental Verification

Abstract

Objectives 1. State and experimentally verify the law of transmission. 2. State and experimentally verify the law of reflection. 3. Measure reflectance of a mirror. 4. State and experimentally verify Snell's law of refraction. 5. Measure the index of refraction of a solid (polymeric sheet or glass) material using Snell's law of refraction. 6. Examine beam displacers based on plane parallel plates. 7. Experimentally observe the process of total internal reflection. 8. Determine the refractive index of a prism material by measuring the angle of total internal reflection. 9. Formulate the limitations of geometrical optics. Background Many optical devices (glasses, car mirrors, telescopes, projectors, etc.) can be fabricated and understood using the approach of geometrical optics. Within the approximation represented by geometrical optics, light travels in straight lines, or rays. The idea of light rays traveling in straight lines through space is accurate as long as the wavelength of the radiation is much smaller than the windows, passages, and holes that can restrict the path of the light. When this is not true, the phenomenon of diffraction must be considered, and this is the domain of physical optics. Geometrical optics is based on three basic laws: The law of rectilinear propagation (transmission). In a region of constant refractive index n , light travels in a straight line. The law of reflection. When a ray of light is reflected at an interface dividing two optical media, the reflected ray remains within the plane of incidence, and the angle of reflection θ r equals the angle of incidence θ i . The plane of incidence is the plane containing the incident ray and the surface normal at the point of incidence (Fig. 5.1). Mathematically, the law of reflection is very simple: θ r = θ i The law of refraction (Snell's law). When a ray of light is refracted at an interface dividing two transparent media, the transmitted ray remains within the plane of incidence and the sine of the angle of refraction θ t is directly proportional to the sine of the angle of incidence θ i (Fig. 5.1).