Physics
Virtual Image
A virtual image is an optical phenomenon where light appears to diverge from a point behind a mirror or lens, even though no actual light is present at that point. It cannot be projected onto a screen, and its location is determined by tracing the paths of light rays. Virtual images are formed by diverging light rays and are always located on the same side of the mirror or lens as the object.
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6 Key excerpts on "Virtual Image"
eBook - PDF- Rudolf Kingslake(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Similarly, a real object lies outside the system in the usual way, but an object can also be virtual if it is projected into the system by some external means. Of course, in any system containing several refracting surfaces, the image formed by one surface becomes the object for the next, but the terms real and virtual are generally restricted to the original object and final image of a system. Actually, only real images are of any value, and the Virtual Image formed in a microscope becomes a real image on the retina of the observer's eye. Real object Virtual object Real object Real image Real image Virtual Image FIG. 2.1. Real and virtual objects and images. 10 2. LIGHT AND IMAGES D. OBJECT SPACE AND IMAGE SPACE Considered naively, the object space and the image space of a lens system are those spaces containing the object and image, respectively. This is fine if the object and image are real, but if they are virtual, it becomes somewhat confusing. We may regard the object space, no matter where the object itself may be located, as the space containing the incident rays, and likewise the image space as the space containing the emerging rays. Alternatively, we can regard the object space as the space containing the object, but if the object is virtual, we must postulate that the object and image spaces overlap each other to infinity in both directions—a concept that some people find hard to accept. Of course, in a spherical mirror, for example, the entering and reflected rays necessarily lie on the same side of the mirror, and therefore the object and image spaces must be considered to overlap, and the confusion cannot be avoided. II. THE LAW OF REFRACTION Let us consider a plane wave front, in a parallel beam of light, that is incident upon a plane refracting surface, as indicated in Fig. 2.2. At the instant of time when A, the bottom of the wave, touches the surface, then B, the upper end of the wave, will be distant from the surface by FIG.
No longer available |Learn morePhysics for Scientists and Engineers
Foundations and Connections, Extended Version with Modern Physics
- Debora Katz(Author)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
So, in effect, the brain traces these rays back along two straight lines that meet at an imaginary point behind the mirror, but there is no light behind the mirror. (Your bathroom mirror is probably hanging on a wall.) Nevertheless, your brain interprets the point where these rays appear to meet as the location of the image. We define a real image as one in which light rays from every point of an object converge or come together to create every point of the image. This convergence of light rays makes it possible to project a real image on a detector like film, a screen, or your retina. A movie camera lens and a camera obscura both produce real images. By contrast, we call the image produced by your bathroom mirror a Virtual Image. Light rays appear to diverge or spread from every point of a Virtual Image, just as they actually diverge from every point of an object. This divergence of light rays means it is not possible to project a Virtual Image on a screen, just as an object by itself does not project an image. A screen behind your bath- room mirror does not capture your image because there is no light there. A screen facing a bathroom mirror does not capture your image either. Nevertheless, because your eye has a lens, you see a Virtual Image of yourself in a plane mirror. Some curved mirrors produce real images (Section 37-4), but plane mirrors always produce Virtual Images. Finding the Image Formed by a Plane Mirror Your experience looking at your image in a flat mirror provides you with a set of expectations. First, imagine sharing the mirror with a roommate who is standing behind you. Your roommate’s image is behind your image, so we expect that the image distance d i is proportional to the object distance d o . Second, the image is PLANE MIRRORS ▲ Special Case RAY DIAGRAMS Tool VIRTUAL AND REAL IMAGES ★ Major Concept FIGURE 37.15 We have drawn two rays emitted from the tip and two from the base of the object’s arrow.
eBook - PDF- David Halliday, Robert Resnick, Kenneth S. Krane(Authors)
- 2019(Publication Date)
- Wiley(Publisher)
If any of these in- gredients is inconsistent with the others, your brain does the best job it can to make sense of it all. Sometimes, as in the case of “optical illusions,” the brain can be fooled completely. The process is similar when you view light coming from a mirror or lens. Your brain tries to process the infor- mation into the most consistent interpretation it can make. In the case of your image in a plane mirror, for example, your brain seems to want to place you somewhere behind the wall to which your mirror is attached! The type of image that is formed by a plane mirror, and also in some cases by curved mirrors and lenses, is called a Virtual Image. It is characterized by several properties: (1) No light is actually passing through the apparent location of the image. In fact, as in the case of the plane mirror, the image might appear in a location where the light cannot pos- sibly travel. (2) The image cannot be focused on a screen. To see the image, you must look into the mirror or the lens. (3) A Virtual Image produced by a single mirror or lens is al- ways upright (not inverted), although (as we discuss at the end of this chapter) optical systems with two or more lenses or mirrors can produce Virtual Images that may be either up- right or inverted. MIRRORS AND LENSES O ptical systems containing mirrors and lenses are of great practical importance. We can use such systems to correct faulty vision, project an image on a screen where it can be viewed by many people at the same time (such as in a movie theater or in your class- room), and make small objects appear large (as in a microscope) or distant objects appear close (as in a telescope). In this chapter we study the formation of images by mirrors and lenses. We will develop both algebraic and graphical methods for analyzing image formation, and we will extend these methods to systems with two or more components, such as microscopes or telescopes. CHAPTER 40 CHAPTER 40
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
In other cases, the image is a Virtual Image, which cannot be projected onto a screen. Where, for example, is the image formed by eyeglasses? We use ray tracing for thin lenses to illustrate how they form images, and then we develop equations to analyze quantitatively the properties of thin lenses. Consider an object some distance away from a converging lens, as shown in Figure 2.22. To find the location and size of the image, we trace the paths of selected light rays originating from one point on the object, in this case, the tip of the arrow. Chapter 2 | Geometric Optics and Image Formation 73 The figure shows three rays from many rays that emanate from the tip of the arrow. These three rays can be traced by using the ray-tracing rules given above. • Ray 1 enters the lens parallel to the optical axis and passes through the focal point on the opposite side (rule 1). • Ray 2 passes through the center of the lens and is not deviated (rule 2). • Ray 3 passes through the focal point on its way to the lens and exits the lens parallel to the optical axis (rule 3). The three rays cross at a single point on the opposite side of the lens. Thus, the image of the tip of the arrow is located at this point. All rays that come from the tip of the arrow and enter the lens are refracted and cross at the point shown. After locating the image of the tip of the arrow, we need another point of the image to orient the entire image of the arrow. We chose to locate the image base of the arrow, which is on the optical axis. As explained in the section on spherical mirrors, the base will be on the optical axis just above the image of the tip of the arrow (due to the top-bottom symmetry of the lens). Thus, the image spans the optical axis to the (negative) height shown. Rays from another point on the arrow, such as the middle of the arrow, cross at another common point, thus filling in the rest of the image.
eBook - PDFSpatial Augmented Reality
Merging Real and Virtual Worlds
- Oliver Bimber, Ramesh Raskar(Authors)
- 2005(Publication Date)
- A K Peters/CRC Press(Publisher)
As illustrated in Figure 2.7(c), objects can also be virtual. In this case, the entering light rays have to be extended to find the location of the corresponding virtual object. Similar to the relationship of the optical path to a Virtual Image, the sub-path to a virtual object also has to be subtracted from the total path length. The production of absolute optical systems is difficult, since the only surfaces that are easy to build and support stigmatism (some only for a single object-image pair) are planar or spherical surfaces. Therefore, most optical instruments only approximate stigmatic image formation. The in-troduced deviation from the ideal image is called aberration . Some exam-ples of reflective and refractive optical systems are given in the following sections. 2.2.3 Reflective Optics In the case of exclusively reflective optical systems ( mirrors ), the medium that light rays travel through is homogeneous, thus η 1 = η 2 = η and 2.2. Geometric Optics 21 i x = j x . Consequently, the optical path length equation can be simplified: L ( p o → p i ) = η (( i x − p o ) + ( p i − i x )) = const . It can be further idealized that a mirror is surrounded by air, and that the medium air is approximately equivalent to the medium of a vacuum ( η = 1), then two stigmatic points which are formed within air are defined by L ( p o → p i ) = ( i x − p o ) + ( p i − i x ) = const . Planar mirrors. In the case of planar mirrors p o is real while p i is virtual (Figure 2.8 (a)), and all points i x of the simplified optical path equation describe the surface of a rotation-hyperboloid with its two focal points in p o and p i . Planes represent a special variant of a rotation-hyperboloid, where L ( p o → p i ) = 0. Planar mirrors are absolute optical systems that map each object p o to exactly one image p i . Since this mapping is bijective, invertible, and symmetrical for all points, it provides stigmatism between all objects and images.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
d o is 2 if the object is behind the mirror (virtual object).* *Sometimes optical systems use two (or more) mirrors, and the image formed by the first mirror serves as the object for the second mirror. Occasionally, such an object falls behind the second mirror. In this case the object distance is negative, and the object is said to be a virtual object. R 5 22f (1) (2) f 5 a 1 d o 1 1 d i b 21 ? Concept Summary 715 CONCEPT SUMMARY 25.1 Wave Fronts and Rays Wave fronts are surfaces on which all points of a wave are in the same phase of motion. Waves whose wave fronts are flat surfaces are known as plane waves. Rays are lines that are perpendicular to the wave fronts and point in the direction of the velocity of the wave. 25.2 The Reflection of Light When light reflects from a smooth surface, the reflected light obeys the 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 u r equals the angle of incidence u i (u r 5 u i ). 25.3 The Formation of Images by a Plane Mirror A Virtual Image is one from which all the rays of light do not actually come, but only appear to do so. A real image is one from which all the rays of light actually do emanate. A plane mirror forms an upright, Virtual Image that is located as far behind the mirror as the object is in front of it. In addition, the heights of the image and the object are equal. 25.4 Spherical Mirrors A spherical mirror has the shape of a section from the surface of a hollow sphere. If the inside surface of the mirror is polished, it is a concave mirror. If the outside surface is polished, it is a convex mirror. The principal axis of a mirror is a straight line drawn through the center of curvature and the middle of the mirror’s surface. Rays that are close to the principal axis are known as paraxial rays. Paraxial rays are not necessarily parallel to the principal axis.
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