Ch 35 Reflection and Refraction of Light.ppt

OPTICS Chapter 33 Geometrical Optics Optics is the study of the behavior of light (not necessarily visible light). This behavior can be described by Maxwell’s equations. However, when the objects with which light interacts are larger that its wavelength,the light travels in straight lines called rays, and its wave nature can be ignored. This is the realm of geometrical optics. The wave properties of light show up inphenomena such as interference and diffraction. Geometrical Optics Reflection and Transmission Reflection The Law of Reflection: Light reflected from a surface stays in the plane formed by the incident ray and the surface normal; and the angle of reflection equals the angle of incidence (measured to the normal) Refraction Refraction Refraction Total Internal Reflection Suppose the light goes from medium 1 to 2 and that n2n1 (for example, from water to air). Snell’s law gives sin q2 = (n1 / n2) sin q1. Since sin q2 = 1 there must be a maximum value of q1. At angles bigger than this “critical angle”, the beam is totally reflected. The critical angle is when q2=p/2, which gives qc=sin-1(n2/n1). Example: Fiber Optics Reflection and Transmission at Normal Incidence Reflection and Transmission at Oblique Incidence Reflection and Transmission at Oblique Incidence Reflection and Transmission at Oblique Incidence Reflection and Refraction Light can be described using geometrical optics, as long as the objects with which it interacts, are much larger than the wavelength of the light. This can be described using geometrical optics This requires the use of full wave optics (Maxwell’s equations) Some materials reflect light. For example, metals reflect light because an incident oscillating light beam causes the metal’s nearly free electrons to oscillate, setting up another (reflected) electromagnetic wave. Opaque materials absorb light (by, say, moving electrons into higher atomic orbitals). Transparent materials are usually insulators whose electron