医学物理学 第十周周五物理chapter 7a_13.ppt

Chapter 7 Geometrical Optics (general theory) 7.1 Reflection and Refraction Medical Fibrescopes 7.2 Refraction of a spherical surface and coaxial spherical system 7.3 Thin lenses Some questions for you to answer Summary to the last lecture when the rod is in air, n1 = 1.0, n2 = 1.5, r = 20mm, u = 80 mm. Substituting these known conditions into the equation of single spherical surface, we have: We know that if the rays emitted from an object are refracted and parallel to the axis, the object distance is called the first focal distance. On the other hand, if the object is at infinity, the image should be at focus on the other side of the lens, the image distance is called the second focal distance. They should be A lens is a simple coaxial system and it is an optical system including two refracting surfaces. If the thickness of a lens is much smaller than curvature radius, the object and image distances, the thickness of the lens can be negligible in comparison with them. Such a lens is called thin lens. Lens can converge and diverge light. 7.3.1 Some special rays for converging and diverging lenses (1). Light rays parallel to the axis of a converging lens are refracted through the focal point on the opposite side of the lens. First and second focal point of a lens. Planes through the focal points of a lens are called focal planes. (2). Light rays parallel to the axis of a diverging lens are refracted so that their backward continuations (extension) pass through the focal point on the same side of the lens. (3) Definition of converging and diverging lenses A lens is converging if the glass is thinner around the circumference than at the center and diverging if the situation is reversed. (4). Graphical method A light ray through the center of a thin lens continues un-deviated and un-displaced. A light ray parallel to the axis passes through the second focal point of a converging lens F Real image Virtual image 7.3.2 The lens equation u v1 v n0 n n0 Ac