Physics
Electromagnetic Waves
Electromagnetic waves are a form of energy that propagate through space, consisting of oscillating electric and magnetic fields. They can travel through a vacuum and do not require a medium for transmission. Electromagnetic waves include a wide range of frequencies, from radio waves to gamma rays, and are fundamental to various phenomena, including light and wireless communication.
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9 Key excerpts on "Electromagnetic Waves"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter 6 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ____________________ WORLD TECHNOLOGIES ____________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic Waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
eBook - PDF- Paul Peter Urone, Roger Hinrichs(Authors)
- 2012(Publication Date)
- Openstax(Publisher)
The list of the various types of Electromagnetic Waves, ranging from radio transmission waves to nuclear gamma-ray ( γ -ray) emissions, is interesting in itself. Even more intriguing is that all of these widely varied phenomena are different manifestations of the same thing—Electromagnetic Waves. (See Figure 24.2.) What are Electromagnetic Waves? How are they created, and how do they Chapter 24 | Electromagnetic Waves 953 travel? How can we understand and organize their widely varying properties? What is their relationship to electric and magnetic effects? These and other questions will be explored. Misconception Alert: Sound Waves vs. Radio Waves Many people confuse sound waves with radio waves, one type of electromagnetic (EM) wave. However, sound and radio waves are completely different phenomena. Sound creates pressure variations (waves) in matter, such as air or water, or your eardrum. Conversely, radio waves are Electromagnetic Waves, like visible light, infrared, ultraviolet, X-rays, and gamma rays. EM waves don’t need a medium in which to propagate; they can travel through a vacuum, such as outer space. A radio works because sound waves played by the D.J. at the radio station are converted into Electromagnetic Waves, then encoded and transmitted in the radio-frequency range. The radio in your car receives the radio waves, decodes the information, and uses a speaker to change it back into a sound wave, bringing sweet music to your ears. Discovering a New Phenomenon It is worth noting at the outset that the general phenomenon of Electromagnetic Waves was predicted by theory before it was realized that light is a form of electromagnetic wave. The prediction was made by James Clerk Maxwell in the mid-19th century when he formulated a single theory combining all the electric and magnetic effects known by scientists at that time. “Electromagnetic Waves” was the name he gave to the phenomena his theory predicted.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 5 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ________________________ WORLD TECHNOLOGIES ________________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic Waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 6 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a phenol-menon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ____________________ WORLD TECHNOLOGIES ____________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic Waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa . Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form an electromagnetic wave. ________________________ WORLD TECHNOLOGIES ________________________ A quantum theory of the interaction between electromagnetic radiation and matter such as electrons is described by the theory of quantum electrodynamics. Properties Electromagnetic Waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized wave propagating from right to left. The electric field is in a vertical plane and the magnetic field in a horizontal plane. The physics of electromagnetic radiation is electrodynamics. Electromagnetism is the physical phenomenon associated with the theory of electrodynamics. Electric and magnetic fields obey the properties of superposition so that a field due to any particular particle or time-varying electric or magnetic field will contribute to the fields present in the same space due to other causes: as they are vector fields, all magnetic and electric field vectors add together according to vector addition. For instance, a travelling EM wave incident on an atomic structure induces oscillation in the atoms of that structure, thereby causing them to emit their own EM waves, emissions which alter the impinging wave through interference. These properties cause various phenomena including refraction and diffraction.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
24.1 | The Nature of Electromagnetic Waves In Section 13.3 we saw that energy is transported to us from the sun via a class of waves known as Electromagnetic Waves. This class includes the familiar visible, ultraviolet, and infrared waves. In Sections 18.6, 21.1, and 21.2 we studied the concepts of electric and magnetic fields. It was the great Scottish physicist James Clerk Maxwell (1831–1879) who showed that these two fields fluctuating together can form a propagating electromagnetic wave. We will now bring together our knowledge of electric and magnetic fields in order to understand this important type of wave. Figure 24.1 illustrates one way to create an electromagnetic wave. The setup con- sists of two straight metal wires that are connected to the terminals of an ac generator and serve as an antenna. The potential difference between the terminals changes sinus- oidally with time t and has a period T. Part a shows the instant t 5 0 s, when there is no charge at the ends of either wire. Since there is no charge, there is no electric field at the point P just to the right of the antenna. As time passes, the top wire becomes positively charged and the bottom wire negatively charged. One-quarter of a cycle later ( t 5 1 4 T ), the charges have attained their maximum values, as part b of the drawing indicates. The corresponding electric field E B at point P is represented by the red arrow and has increased to its maximum strength in the downward direction.* Part b also shows that the electric field created at earlier times (see the black arrow in the picture) has not dis- appeared but has moved to the right. Here lies the crux of the matter: At distant points, the electric field of the charges is not felt immediately. Instead, the field is created first near the wires and then, like the effect of a pebble dropped into a pond, moves outward as a wave in all directions. Only the field moving to the right is shown in the picture for the sake of clarity.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Electromagnetic Waves can travel through a vacuum or a material substance, since electric and magnetic fields can exist in either one. Electromagnetic Waves can be produced in situations that do not involve a wire antenna. In general, any electric charge that is accelerating emits an electromagnetic wave, whether the charge is inside a wire or not. In an alternating current, an electron (a) t = 0 s P (b) t = T E P (c) P (d) P (e) t = T P + + + + – – – – 1 4 t = T 2 4 t = T 3 4 ANIMATED FIGURE 24.1 In each part of the drawing, the red arrow represents the electric field → E produced at point P by the oscillating charges on the antenna at the indicated time. The black arrows represent the electric fields created at earlier times. For simplicity, only the fields propagating to the right are shown. *The direction of the electric field can be obtained by imagining a positive test charge at P and determi- ning the direction in which it would be pushed because of the charges on the wires. B I P I FIGURE 24.2 The oscillating current I in the antenna wires creates a magnetic field → B at point P that is tangent to a circle centered on the wires. The field is directed as shown when the current is upward and is directed in the opposite direction when the current is downward. 24.1 The Nature of Electromagnetic Waves 761 y z x B E Direction of wave travel FIGURE 24.3 This picture shows the wave of the radiation field far from the antenna. Observe that → E and → B are perpendicular to each other, and both are perpendicular to the direction of travel. oscillates in simple harmonic motion along the length of the wire and is one example of an accelerating charge. All Electromagnetic Waves move through a vacuum at the same speed, and the symbol c is used to denote its value. This speed is called the speed of light in a vacuum and is c = 3.00 × 10 8 m/s.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
LEARNING OBJECTIVES After reading this module, you should be able to... 24.1 Describe the nature of Electromagnetic Waves. 24.2 Calculate speed, frequency, and wavelength for Electromagnetic Waves. 24.3 Relate the speed of light to electromagnetic quantities. 24.4 Calculate energy, power, and intensity for Electromagnetic Waves. 24.5 Solve problems involving the Doppler effect for Electromagnetic Waves. 24.6 Solve polarization problems using Malus’ law. Terje Rakke/Getty Images CHAPTER 24 Electromagnetic Waves Each of the colors on the sails of these boats corresponds to a different wavelength in the visible region of the spectrum of Electromagnetic Waves. As we will see in this chapter, however, the visible wavelengths comprise only a small part of the total electromagnetic spectrum. 24.1 The Nature of Electromagnetic Waves In Section 13.3 we saw that energy is transported to us from the sun via a class of waves known as Electromagnetic Waves. This class includes the familiar visible, ultra- violet, and infrared waves. In Sections 18.6, 21.1, and 21.2 we studied the concepts of electric and magnetic fields. It was the great Scottish physicist James Clerk Maxwell (1831–1879) who showed that these two fields fluctuating together can form a propagating electromagnetic wave. We will now bring together our knowledge of electric and magnetic fields in order to understand this important type of wave. Animated Figure 24.1 illustrates one way to create an electromagnetic wave. The setup consists of two straight metal wires that are connected to the terminals of an ac generator and serve as an antenna. The potential difference between the terminals changes sinusoidally with time t and has a period T. Part a shows the instant t = 0 s, when there is no charge at the ends of either wire. Since there is no charge, there is no electric field at the point P just to the right of the antenna.
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)
24.2 Calculate speed, frequency, and wavelength for Electromagnetic Waves. The frequency f and wavelength of an electromagnetic wave in a vacuum are related to its speed c through the relation c = f. The series of Electromagnetic Waves, arranged in order of their frequencies or wavelengths, is called the electromagnetic spectrum. In increasing order of frequency (decreasing order of wavelength), the spectrum includes radio waves, infrared radiation, visible light, ultraviolet radiation, X‐rays, and gamma rays. Visible light has frequencies between about 4.0 × 10 14 and 7.9 × 10 14 Hz. The human eye and brain perceive different frequencies or wavelengths as different colours. 24.3 Relate the speed of light to electromagnetic quantities. James Clerk Maxwell showed that the speed of light in a vacuum is given by equation 24.1, where 0 is the (electric) permittivity of free space and 0 is the (magnetic) permeability of free space. c = 1 √ 0 0 (24.1) 24.4 Calculate energy, power, and intensity for Electromagnetic Waves. The total energy density u of an electromagnetic wave is the total energy per unit volume of the wave and, in a vacuum, is given by equation 24.2a, where E and B, respectively, are the magnitudes of the electric and magnetic fields of the wave. Since the electric and magnetic parts of the total energy density are equal, equations 24.2b and 24.2c are equivalent to equation 24.2a. In a vacuum, E and B are related according to equation 24.3. u = 1 2 0 E 2 + 1 2 0 B 2 (24.2a) u = 0 E 2 (24.2b) u = 1 0 B 2 (24.2c) E = cB (24.3) Equations 24.2a–24.2c can be used to determine the average total energy density, if the rms average values E rms and B rms are used in place of the symbols E and B. The rms values are related to the peak values E 0 and B 0 in the usual way, as shown in equations 1 and 2. The intensity of an electromagnetic wave is the power that the wave carries perpendicularly through a surface divided by the area of the surface.
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