Physics
Reflection
Reflection in physics refers to the change in direction of a wavefront at an interface between two different media, such as air and water. This change occurs because the wavefront bounces back after hitting the boundary. The angle of incidence is equal to the angle of reflection, and this principle is used in various optical devices and phenomena.
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12 Key excerpts on "Reflection"
eBook - PDF- James Shipman, Jerry Wilson, Charles Higgins, Bo Lou, James Shipman(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
A change in direction takes place when light strikes and rebounds from a surface. A change in direction by this method is called Reflection. Reflection may be thought of as light “bouncing off” a surface. However, it is much more complicated and involves the absorption and emission of complex atomic vibra- tions of the reflecting medium. To describe Reflection simply, the Reflection of rays is considered, which ignores the wave nature of light. A ray is a straight line that represents the path of light with a directional arrowhead. An incident light ray is reflected from a surface in a particular way. As illustrated in ●●Fig. 7.1, the angles of the incident and reflected rays (u i and u r ) are measured relative to the normal, a line perpendicular to the reflecting surface. These angles are related by the law of Reflection: The angle of Reflection u r is equal to the angle of incidence u i . Also, the reflected and incident rays are in the same plane. Figure 7.1 Law of Reflection The angle of Reflection u r is equal to the angle of incidence u i relative to the normal (a line perpendicular to the reflecting surface). The rays and the normal line lie in the same plane. Incident ray Reflecting surface Reflected ray Normal u i u r u i u r = Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 168 Chapter 7 ● Optics and Wave Effects Diffuse (irregular) Reflection (b) Specular (regular) Reflection (a) Figure 7.2 Reflection (a) A smooth (mirror) surface produces specular (or regular) Reflection. (b) A rough surface produces diffuse (or irregular) Reflection.
eBook - PDF- Graham Saxby(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
The Science of Imaging, Second Edition: An Introduction 12 that is symmetrical with respect to the surface. In practice we don’t use the surface as our reference, because it may be (indeed, usually is) curved. Instead, we use the perpendicular at the reference point, called the normal . We can use a simple geometrical model here. Instead of the tedious business of drawing wave-fronts we can simply draw a line showing the direction in which they are travel-ling, a ray . Reflection is then a straightforward matter. The angle the entering (incident) ray makes with the normal is called the angle of incidence , and the angle the emerging (reflected) ray makes with it is called the angle of Reflection (Figure 1.13). The two laws of Reflection are: 1. The incident and reflected rays are in the same plane as the normal. 2. The angle of incidence is equal to the angle of Reflection. These laws also apply to curved surfaces, and here it is much easier to follow the path of a light beam by using rays rather than wavefronts. The term refraction refers to the change in direction of a light beam entering a substance having optical qualities different from the one it has left. The speed of light discussed earlier was actually the speed of light in empty space. In air this is very slightly less, and in liquids and transparent solids it is very much less. When a beam of light enters a glass block obliquely, the wavefront is slowed down, and successive crests become closer together. There is thus a change in direction of the wavefront towards the normal. On emergence from a parallel surface the process is reversed, and the beam resumes its original direction (Figure 1.14). The change in direction is called refraction . Again, we can simplify the geometry by using the ray model. As in Reflection, the incident ray, the refracted ray, and the normal are all in the same plane.
eBook - PDF- Richard L. Myers(Author)
- 2005(Publication Date)
- Greenwood(Publisher)
The remainder of this chapter will focus on the classical theory of light. Behavior of Light In the previous section, a number of properties of light were introduced. Since several of these are associated with other wave phenomena, they were discussed in the last chapter with respect to sound, for example, refraction, Reflection, and interfer- ence. In this section, these and several other properties unique to light are explored. The wave properties of light are often discussed by examining wave fronts and light rays. Wave fronts consist of an imaginary line drawn along all points in phase. For exam- ple, when standing on the shore and watch- ing waves, the wave fronts are represented by crests running parallel to shore that break regularly. A light ray is a line drawn per- pendicular to wave fronts. If light waves are considered analogous to ripples created by dropping a pebble into water, the wave fronts spread out from the source as shown in Figure 9.2. As these ripples spread out from their source, the wave fronts become flatter and approach a parallel configuration. Rays are imaginary lines from the source perpendicular to the wave fronts. As the waves move farther away, the wave fronts move from a spherical to a planar shape. Therefore, at a certain distance, wave fronts can be considered parallel planes with rays that are perpendicular. Reflection Reflection is one of the most obvious properties of light. Mirrors are commonly 152 Light and Optics used in a variety of instruments to apply this property for human use, but Reflection from other surfaces also takes place. Reflection is referenced by referring to the incident rays and reflected rays. Incident rays are the rays before they strike the surface, and reflected rays are the rays after striking the surface (Figure 9.3). The angle of incidence is the angle between an incident ray and a nor- mal drawn perpendicular to the reflecting surface.
- Raymond Serway, John Jewett(Authors)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
As with Reflection, the direction of the transmitted wave exhibits an interesting behavior because of the three-dimensional nature of the light waves. The ray that enters the sec- ond medium changes its direction of propagation at the boundary, bend- ing toward or away from the normal, and is said to be refracted. The inci- dent ray, the reflected ray, and the refracted ray all lie in the same plane. The angle of refraction, u 2 in Figure 34.10a, depends on the properties of the two media and on the angle of incidence u 1 through the relationship sin u 2 sin u 1 5 v 2 v 1 (34.2) where v 1 is the speed of light in the first medium and v 2 is the speed of light in the second medium. We have stated this equation without proof, but it will be derived in Section 34.5. Q UICK QUIZ 34.2 If beam ➀ is the incoming beam in Figure 34.10b, which of the other four red lines are reflected beams and which are refracted beams? Glass Air A B Incident ray Normal Reflected ray Refracted ray u 1 v 1 v 2 u 2 a All rays and the normal lie in the same plane, and the refracted ray is bent toward the normal because v 2 v 1 . u' 1 b Courtesy of Henry Leap and Jim Lehman Figure 34.10 (a) The wave under refrac- tion model. (b) Light incident on the Lucite block refracts both when it enters the block and when it leaves the block. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 906 Chapter 34 The Nature of Light and the Principles of Ray Optics The path of a light ray through a refracting surface is reversible.
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
Its wave characteristics are not pronounced in such situations. Since the wavelength of visible light is less than a micron (a thousandth of a millimeter), it acts like a ray in the many common situations in which it encounters objects larger than a micron. For example, when visible light encounters anything large enough that we can observe it with unaided eyes, such as a coin, it acts like a ray, with generally negligible wave characteristics. In all of these cases, we can model the path of light as straight lines. Light may change direction when it encounters objects (such as a mirror) or in passing from one material to another (such as in passing from air to glass), but it then continues in a straight line or as a ray. The word “ray” comes from mathematics and here means a straight line that originates at some Chapter 1 | The Nature of Light 11 point. It is acceptable to visualize light rays as laser rays. The ray model of light describes the path of light as straight lines. Since light moves in straight lines, changing directions when it interacts with materials, its path is described by geometry and simple trigonometry. This part of optics, where the ray aspect of light dominates, is therefore called geometric optics. Two laws govern how light changes direction when it interacts with matter. These are the law of Reflection, for situations in which light bounces off matter, and the law of refraction, for situations in which light passes through matter. We will examine more about each of these laws in upcoming sections of this chapter. 1.2 | The Law of Reflection Learning Objectives By the end of this section, you will be able to: • Explain the Reflection of light from polished and rough surfaces • Describe the principle and applications of corner reflectors Whenever we look into a mirror, or squint at sunlight glinting from a lake, we are seeing a Reflection. When you look at a piece of white paper, you are seeing light scattered from it.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
The rays are perpendicular to the wave fronts and point in the direction of the velocity of the wave. 628 Chapter 25 | The Reflection of Light: Mirrors 25.2 | The Reflection of Light Most objects reflect a certain portion of the light falling on them. Suppose that a ray of light is incident on a flat, shiny surface, such as the mirror in Figure 25.3. As the drawing shows, the angle of incidence u i is the angle that the incident ray makes with respect to the normal, which is a line drawn perpendicular to the surface at the point of incidence. The angle of reflection u r is the angle that the reflected ray makes with the normal. The law of reflection describes the behavior of the incident and reflected rays. When parallel light rays strike a smooth, plane surface, such as the ones in Figure 25.4a, the reflected rays are parallel to each other. This type of reflection is one example of what is known as specular reflection and is important in determining the properties of mirrors. Most surfaces, however, are not perfectly smooth, because they contain irregularities the sizes of which are equal to or greater than the wavelength of the light. The law of reflection applies to each ray, but the irregular surface reflects the light rays in various directions, as Figure 25.4b suggests. This type of reflection is known as diffuse reflection. Common surfaces that give rise to diffuse reflection are most papers, wood, nonpolished metals, and walls covered with a “flat” (nongloss) paint. The physics of digital movie projectors and micromirrors. A revolution in digital tech- nology is occurring in the movie industry, where digital techniques are now being used to produce films. Until recently, films have been viewed primarily by using projectors that shine light directly through a strip of film containing the images.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
The rays are perpendicular to the wave fronts and point in the direction of the velocity of the wave. 700 Chapter 25 | The Reflection of Light: Mirrors 25.2 | The Reflection of Light Most objects reflect a certain portion of the light falling on them. Suppose that a ray of light is incident on a flat, shiny surface, such as the mirror in Figure 25.3. As the drawing shows, the angle of incidence u i is the angle that the incident ray makes with respect to the normal, which is a line drawn perpendicular to the surface at the point of incidence. The angle of reflection u r is the angle that the reflected ray makes with the normal. The law of reflection describes the behavior of the incident and reflected rays. When parallel light rays strike a smooth, plane surface, such as the ones in Figure 25.4a, the reflected rays are parallel to each other. This type of reflection is one example of what is known as specular reflection and is important in determining the properties of mirrors. Most surfaces, however, are not perfectly smooth, because they contain irregularities the sizes of which are equal to or greater than the wavelength of the light. The law of reflection applies to each ray, but the irregular surface reflects the light rays in various directions, as Figure 25.4b suggests. This type of reflection is known as diffuse reflection. Common surfaces that give rise to diffuse reflection are most papers, wood, nonpolished metals, and walls covered with a “flat” (nongloss) paint. The physics of digital movie projectors and micromirrors. A revolution in digital tech- nology is occurring in the movie industry, where digital techniques are now being used to produce films. Until recently, films have been viewed primarily by using projectors that shine light directly through a strip of film containing the images.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler, Heath Jones, Matthew Collins, John Daicopoulos, Boris Blankleider(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
CHAPTER 25 The Reflection of light: mirrors LEARNING OBJECTIVES After reading this module, you should be able to: 25.1 relate wave fronts and rays 25.2 apply the law of Reflection to plane mirrors 25.3 describe image formation by a plane mirror 25.4 calculate the focal length of a spherical mirror 25.5 perform ray tracing for spherical mirrors 25.6 use the mirror and magnification equations to solve problems. INTRODUCTION Amateur and professional astronomers benefit from the light gathered to create images formed by the most versatile telescopes ever built — reflectors. This chapter discusses how images are created by the Reflection of light from plane and spherical mirrors. 25.1 Wave fronts and rays LEARNING OBJECTIVE 25.1 Relate wave fronts and rays. FIGURE 25.1 A hemispherical view of a sound wave emitted by a pulsating sphere. The wave fronts are drawn through the condensations of the wave, so the distance between two successive wave fronts is the wavelength . The rays are perpendicular to the wave fronts and point in the direction of the velocity of the wave. l Wave fronts Pulsating sphere Rays Mirrors are usually close at hand. It is difficult, for example, to put on makeup, shave, or drive a car without them. We see images in mirrors because some of the light that strikes them is reflected into our eyes. To discuss Reflection, it is necessary to introduce the concepts of a wave front and a ray of light, and we can do so by taking advantage of the familiar topic of sound waves (see chapter 16). Both sound and light are kinds of waves. Sound is a pressure wave, whereas light is electromagnetic in nature. However, the ideas of a wave front and a ray apply to both. Consider a small spherical object whose surface is pulsating in simple harmonic motion. A sound wave is emitted that moves spherically outwards from the object at a constant speed. To represent this wave, we draw surfaces through all points of the wave that are in the same phase of motion.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
Since rays are perpendicular to the wave fronts, the rays for a plane wave are parallel to each other. The concepts of wave fronts and rays can also be used to describe light waves. For light waves, the ray concept is particularly convenient when showing the path taken by the light. We will make frequent use of light rays, which can be regarded essentially as narrow beams of light much like those that lasers produce. 25.2 The Reflection of Light Most objects reflect a certain portion of the light falling on them. Suppose that a ray of light is incident on a flat, shiny surface, such as the mirror in Figure 25.3. As the drawing shows, the angle of incidence i is the angle that the incident ray makes with respect to the normal, which is a line drawn perpendicular to the surface at the point of incidence. The angle of reflection r is the angle that the reflected ray makes with the normal. The law of reflection describes the behavior of the incident and reflected rays. LAW OF Reflection The incident ray, the reflected ray, and the normal to the surface all lie in the same plane, and the angle of reflection r equals the angle of incidence i : r = i When parallel light rays strike a smooth, plane surface, such as the ones in Figure 25.4a, the reflected rays are parallel to each other. This type of reflection is one example of what is known as specular reflection and is important in determining the properties of mirrors. Most surfaces, however, are not perfectly smooth, because they contain irregularities the sizes of which are equal to or greater than the wavelength of the light. The law of reflection applies to each ray, but the irregular surface reflects the light rays in various directions, as Figure 25.4b suggests. This type Normal Incident ray Mirror i r Reflected ray θ θ FIGURE 25.3 The angle of reflection r equals the angle of incidence i .
eBook - PDF- Raimo Silvennoinen, Kai-Erik Peiponen, Kari Myller(Authors)
- 2010(Publication Date)
- Elsevier Science(Publisher)
Chapter 2 LIGHT Reflection FROM IDEAL SURFACE The spectrum of electromagnetic radiation ranges from zero energy up to high energies corresponding to gamma rays. In that sense, the wavelength range of visible light is rather narrow. Nevertheless, this short range of visible light is crucial because it defines the spectral window of a human eye. Hence, much of the assessment of quality of various objects, such as indus-trial products, is based on purely visual inspection of the objects. We can detect the shape and colour of an object and estimate local changes of such attributes. One important factor that helps us to estimate the qual-ity of smooth and rough surfaces is the specular gloss. For instance, illumination of a planar mirror or a win-dow by a torch results in light Reflection in specular direction (mirror Reflection). Mirror surface is smooth and therefore resembles an ideal surface that is usu-ally exploited in the development of laws of geometric optics. The concept of an ideal surface constitutes also the fundamental assumption in wave optics as concerns the Reflection of light from the interface between two media or a stack of layers. In this chapter, we deal with the light interaction with an ideally smooth sur-face. We introduce the basic concepts that are needed in the description of the light propagation and light interaction with media. 6 Specular Gloss 2.1. Electromagnetic theory of light waves 2.1.1. Wave equation It is well known that the radio waves have been for a long time used for transmission of information from one place to another. During the last decades, light waves in the form of pulses have been exploited in telecommunication through optical fibres, thanks to the development of LEDs and lasers. Let us start by considering one-dimensional (1-D) wave motion. Note that in some cases, one dimensiona-lity means that 2-D or 3-D wave motion can be described only with one spatial coordinate.
eBook - PDFAnd Yet It Moves
Strange Systems and Subtle Questions in Physics
- Mark P. Silverman(Author)
- 1993(Publication Date)
- Cambridge University Press(Publisher)
144 Reflections on light 4.2 Enhanced Reflection: how light gets brighter when it is up against a wall A light beam incident upon a transparent material is partially transmit- ted through the surface and refracted (i.e. deviated from its original direction), and partially reflected from the surface. The exact division of light energy between these two processes was first worked out in the early 1820s - that is, long before the electromagnetic theory of light - by the French physicist and engineer, Augustin Fresnel, whose name, like that of Maxwell's, is associated with a variety of inventions, discoveries and principles. Along with the Englishman Thomas Young, Fresnel was a major contributor to the perception of light as a wave-like phenomenon. Fresnel regarded light waves as a type of elastic wave like that of sound passing through air or of ripples spreading on the surface of water. Since all elastic waves require a medium, Fresnel assumed that the light propagated through an extremely tenuous hypothetical medium, the aether, that permeated all space and penetrated all objects. Not until many years later, after Einstein developed the theory of special relativity in 1905, were most physicists fully prepared to dis- pense with the concept of the aether. Nevertheless, Fresnel's elastic theory enabled him to predict or account for many aspects of the behaviour of light. In the course of his investigations of light polaris- ation, Fresnel deduced the amplitudes (relative to an incident light wave of unit amplitude) of light specularly reflected and refracted at the surface of a transparent medium. (Specular Reflection is 'mirror-like' Reflection from a smooth surface, in contrast to diffuse Reflection from a rough surface.) These amplitudes are ordinarily designated the Fresnel relations or Fresnel coefficients.
eBook - PDF- Y K Lim(Author)
- 1986(Publication Date)
- WSPC(Publisher)
Chapter V Reflection AND REFRACTION OF PLANE ELECTROMAGNETIC WAVES When an electromagnetic wave passes through the boundary between two different media, Reflection and refraction occur. The consequent change of direction, phase and intensity may all be derived from the boundary conditions governing the change of the associated field vectors. 5.1 Laws of Reflection and Refraction We have seen in Sec. 2.8 that the electric field of a plane electromagnetic wave travelling parallel to the x-axis in a linear, isotropic and homogeneous medium of permittivity e and permeability u can be represented by either E (x-vt) or E (x-vt), or their vector sum, where E and E are arbitrary functions of x-vt, and v= (ue) is the phase velocity of the wave in the medium. It is often desirable to have a more general representation. Let o be the origin and k a unit vector in the direction of propagation, then -* c-for a point P in the path of the wave, OP=xk. If o' is the new + -*■ origin and we denote oo' = r , 0'P= r, then as shown in Fig. 5.1 we have Hence xfi = r + r x -vt = k • r + k • r - vt = k • r + I (k • r -
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