Lecture 12Light Reflection and Refraction.ppt

Lecture 12Light: Reflection and Refraction Towards the Nature of Light What is Light? Geometric Optics Reflection of Light Refraction of Light The Law of Refraction The Law of Refraction A Refraction Problem Summary Light is a form of electromagnetic waves. It shows properties of both a wave and a particle. Reflection and refraction are wave properties of light. For specular reflection, the angle of incidence equals to the angle of reflection Index of refraction is a property of a medium. It is a measure of the speed of light in a certain medium. * Chapter 22.1 ? 22.4 Outline History of Studies of Light Reflection of Light The Law of Refraction. Index of Refraction. Newton considered light as a stream of particles and explained reflection and refraction (1660s). Huygens proved that these phenomena can be understood if light is waves (1670s). Grimaldi (ca. 1660) and Young (1801) experimentally demonstrated that light exhibits diffraction and interference. Maxwell (1865) predicted that light is a form of electromagnetic waves. Work of Hertz (1880s), Planck (1900), and Einstein (1905) showed that light has dual nature. Dual nature means that under some conditions light behaves as a wave, while under others as a particle. Light does not show properties of both wave and particle in the same experiment. Particles of light are called photons. E = h f E ? energy of a photon h = 6.63 10?34 J s ? Planck constant f ? frequency of the electromagnetic wave Light travels in a straight-line path in a homogeneous medium. At a boundary between 2 different media the light: is reflected passes into the other medium (material) does both (partially) After entering a different medium, light continues traveling in a straight-line path. Definition: wave front is a surface of a wave with the same phase and amplitude. There are types of reflection: specular and diffuse. Picture ?? = ? Reflection off a smooth surface (average distance between irregularities is smaller than the wavelength o