Science universe: Physics articles

Special Relativity   The special theory of relativity is based on two postulates. 1. The laws of physics are the same in all inertial reference frames. Inertial frames are reference (coordinate) frames moving at constant velocity with respect to one another; that is, they are not accelerating. 2. The speed of light is the same in all inertial frames. These two postulates lead to very interesting and highly significant conclusions concerning simultaneity and how we measure the fundamental quantities of length, mass, and time. These discussions, though very interesting, are inappropriate for a problems book, so we will go directly to the consequences of special relativity as it impacts our understanding of physics. The concepts and calculations of special relativity require a change in how we view the world. Many of the things we study in special relativity may go against our intuition, but remember, intuition is often wrong and even if it were correct we have no experienc...

Diffraction and Interference   The wave nature of light is used to explain the several diffraction and interference phenomena discussed in this chapter.   Double Slit Diffraction Figure 46-1 shows the setup for the classic Young's double slit experiment first performed around 1800.   Fig. 46-1   Monochromatic light passes through a sufficiently narrow slit to produce a coherent source for the double slits. The coherent (in phase) light spreads out from each of the slits creating an interference pattern on the screen. The geometry for the interference is shown in Fig. 46-1. Destructive interference occurs when the path length differs by one-half wavelength and constructive interference occurs when the path length is an integral number of wavelengths. From the figure we can write the criteria for constructive interference as The distance from the central maxima (opposite the center of the two slits) to the first bright fringe on the screen is related to t...

Mirrors and Lenses The subject of mirrors and lenses is difficult to treat briefly first because for a thorough discussion there needs to be considerable attention to sign convention and second because different instructors and authors approach the subject with slight, but very significant differences that impact the working of problems. The only way to become proficient in working with lenses and mirrors is to place the sign conventions appropriate to your course on a card in front of you and do problems drawing the rays and working the calculations. Be sure that you know the sign conventions and practice doing sample problems before taking any tests on mirrors or lenses. Signs will be your major (perhaps only) source of error. Sample sign conventions for mirrors and lenses are given below. Sign Conventions for Mirrors   o is positive if object is in front of the mirror o is negative if object is in back of the mirror   i is positive if the image is in front of ...