Physics
Mirror Waves
Mirror waves are a type of electromagnetic wave that can be observed in space. They are created when a plasma, or ionized gas, interacts with a magnetic field. Mirror waves are important for understanding the behavior of charged particles in space and can have implications for space weather and spacecraft operations.
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5 Key excerpts on "Mirror Waves"
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
25.1 | Wave Fronts and 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 con- cepts 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 mo- tion. A sound wave is emitted that moves spherically outward 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. These surfaces of constant phase are called wave fronts. Figure 25.1 shows a hemispherical view of the wave fronts. In this view they appear as concentric spherical shells about the vibrating object. If the wave fronts are drawn through the condensations, or crests, of the sound wave, as they are in the picture, the distance between adjacent wave fronts equals the wavelength l. The radial lines pointing outward from the source and perpendicular to the wave fronts are called rays. The rays point in the direction of the velocity of the wave. Figure 25.2a shows small sections of two adjacent spherical wave fronts. At large distances from the source, the wave fronts become less and less curved and approach the shape of flat surfaces, as in part b of the drawing. Waves whose wave fronts are flat surfaces (i.e., planes) are known as plane waves and are important in understanding the properties of mirrors and lenses. Since rays are perpendicular to the wave fronts, the rays for a plane wave are parallel to each other.
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 -
eBook - PDF- John Matolyak, Ajawad Haija(Authors)
- 2013(Publication Date)
- CRC Press(Publisher)
385 © 2010 Taylor & Francis Group, LLC Physical (Wave) Optics 21.1 INTRODUCTION Recall that geometrical optics deals with the properties of light when it encounters objects, mirrors, lenses, and orifices that are large compared with its wavelength. Physical or wave optics addresses light behavior when it encounters objects that are approximately the same size or that are smaller than its wavelength. It is in this realm that light exhibits its wave nature and a wave description of light is appropriate. Under these conditions, the two main manifestations of light behavior are called interference and diffraction . These two phenomena are consequences of a very general principle called the linear superposition principle (LSP). 21.1.1 L INEAR S UPERPOSITION P RINCIPLE A wave is a periodic disturbance in a medium. The medium may be material, as in the case of sound waves traveling through air or a steel rod. Or, it may be nonmaterial as with electromagnetic waves (EMWs), where the medium consists of electric and magnetic fields. It is possible for two or more disturbances (waves) to meet at the same spatial point in a medium, at exactly the same time. Then, the question that arises is how will the medium respond, that is, what is the resultant disturbance at that spatial point and that particular time? The LSP states: The displacement (disturbance) at any point in the medium is equal to the algebraic sum of the indi-vidual displacements (disturbances). For example, consider two EMWs whose oscillations are written as E E sin k x t 1 01 1 1 1 1 = -( ) ω (21.1) and E E sin k x t 2 02 2 2 2 2 = -( ) . ω (21.2) If these two waves meet at some common point, that is, x 1 = x 2 = P, the resultant electric field at P, according to the LSP, is E E E E TOTAL i i 1 2 = = + ∑ . Figure 21.1a depicts two light rays (only the electric field components are shown for clarity) of equal wavelengths, emitted from two separate sources, propagating through air.
- Christopher Lavers(Author)
- 2017(Publication Date)
- Thomas Reed(Publisher)
64 64 4 Wave Properties ‘Aye, I suppose I could stay up that late.’ James Clerk Maxwell , after being informed of a compulsory 6am church service at Cambridge University. In this chapter we will look at some further wave properties that are important when considering electromagnetic waves and their interactions in a real environment, such as polarisation, reflection, refraction and Total Internal Reflection, along with a number of their maritime applications. All of these properties are applicable to acoustic sound waves in the above water environment and sonar acoustic waves underwater, with the exception of polarisation, which is a transverse wave phenomenon only – and it is with polarisation we will begin. 4.1 Polarisation Polarisation occurs only with transverse wave motion. Polarisation is a term describing the alignment of the oscillation direction. Figure 4.1 shows a single electromagnetic wave generated by an oscillating charge. The electric field oscillation in this case is in the vertical direction and is a vector quantity, having both magnitude (size) and direction. If all the electromagnetic waves – and there may be many hundreds of millions of them in a beam from a source such as radar or a laser – have their electric field oscillations all in the same direction, the beam is said to be linearly polarised . Propagation direction out of the page towards the reader Direction of electric fiel d oscillation Figure 4.1: Vertically polarised wave. Wave Properties 65 65 With electromagnetic radiation, if the electric field oscillation is found to be perpendicular to the surface or ground, the beam is described as vertically polarised or transverse magnetic (as the magnetic field component is horizontal), whereas if the electric field is horizontal, the beam is described as horizontally polarised or transverse electric (as the electric field is now horizontal or across the surface).
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.
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