Chemistry
Electric Fields Chemistry
Electric fields in chemistry refer to the force fields that surround charged particles, influencing the behavior of other charged particles within their vicinity. These fields are created by the presence of electric charges and play a crucial role in understanding chemical reactions, particularly those involving ions and polar molecules. Understanding electric fields is essential for comprehending the interactions and behavior of charged species in chemical systems.
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9 Key excerpts on "Electric Fields Chemistry"
- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
630 CHAPTER 22 Electric Fields Our goals in this chapter are to (1) define electric field, (2) discuss how to calculate it for various arrangements of charged particles and objects, and (3) discuss how an electric field can affect a charged particle (as in making it move). The Electric Field A lot of different fields are used in science and engineering. For example, a tem- perature field for an auditorium is the distribution of temperatures we would find by measuring the temperature at many points within the auditorium. Similarly, we could define a pressure field in a swimming pool. Such fields are examples of scalar fields because temperature and pressure are scalar quantities, having only magnitudes and not directions. In contrast, an electric field is a vector field because it is responsible for conveying the information for a force, which involves both magnitude and direc- tion. This field consists of a distribution of electric field vectors E → , one for each point in the space around a charged object. In principle, we can define E → at some point near the charged object, such as point P in Fig. 22.1.2a, with this proce- dure: At P, we place a particle with a small positive charge q 0 , called a test charge because we use it to test the field. (We want the charge to be small so that it does not disturb the object’s charge distribution.) We then measure the electrostatic force F → that acts on the test charge. The electric field at that point is then E → = F → ___ q 0 (electric field). (22.1.1) Because the test charge is positive, the two vectors in Eq. 22.1.1 are in the same direction, so the direction of E → is the direction we measure for F → . The mag- nitude of E → at point P is F/q 0 . As shown in Fig. 22.1.2b, we always represent an electric field with an arrow with its tail anchored on the point where the mea- surement is made.
eBook - PDF- Y K Lim(Author)
- 1986(Publication Date)
- WSPC(Publisher)
Chapter I FUNDAMENTAL CONCEPTS AND EXPERIMENTAL LAWS Electrodynamics deals with the fields and radiation of moving charges. In describing the interaction between charges it is convenient, both mathematically and physically, to consider it, not as forces that act at a distance, but as the force exerted by the field set up by one charge on the other. This approach is in fact essential for charges in relative motion as electromagnetic effects are found to propagate with finite velocity. The four field vectors, Ej B, D and H, which are fundamental in Maxwell's electro-magnetic theory are introduced and discussed in this chapter in a phenomenologiaal manner. In addition, a short review is made of the experimental laws which lead to Maxwell's equations. 1.1 Electric Field Intensity E Electric field is said to exist at a point where a stationary particle experiences a force on account of its charge. The electric field intensity or electric field strength E is defined as the force per unit charge acting on a small positive charge q' introduced at that point. Let F be the electric force acting on the test charge, then by definition 2 . E - lim -L . (1.1) q' + OQ' The limit q' + Q is required in order that the introduction of the test charge will not significantly Influence the source; the field can then be described independently of the presence of a test charge. The finite magnitude of the elementary charge e does not permit the limiting process to be realized even in principle. The definition applies, therefore, to macroscopic phenomena only. For microscopic processes, the field is usually defined in terms of its source, assuming that the macroscopic laws governing the field-source relationship still apply. The simplest type of electric field is one that is set up by stationary charges, the electrostatic field. We shall confine ourselves in the first instance to free space.
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Instead, particle 2 pushes by means of the electric field it has set up. Our goals in this chapter are to (1) define electric field, (2) discuss how to calculate it for various arrangements of charged particles and objects, and (3) dis- cuss how an electric field can affect a charged particle (as in making it move). The Electric Field A lot of different fields are used in science and engineering. For example, a tem- perature field for an auditorium is the distribution of temperatures we would find by measuring the temperature at many points within the auditorium. Similarly, we could define a pressure field in a swimming pool. Such fields are examples of scalar fields because temperature and pressure are scalar quantities, having only magnitudes and not directions. In contrast, an electric field is a vector field because it is responsible for conveying the information for a force, which involves both magnitude and direc- tion. This field consists of a distribution of electric field vectors E → , one for each point in the space around a charged object. In principle, we can define E → at some point near the charged object, such as point P in Fig. 22.1.2a, with this proce- dure: At P, we place a particle with a small positive charge q 0 , called a test charge because we use it to test the field. (We want the charge to be small so that it does not disturb the object’s charge distribution.) We then measure the electrostatic force F → that acts on the test charge. The electric field at that point is then E → = F → ___ q 0 (electric field). (22.1.1) Because the test charge is positive, the two vectors in Eq. 22.1.1 are in the same direction, so the direction of E → is the direction we measure for F → . The mag- nitude of E → at point P is F/q 0 . As shown in Fig. 22.1.2b, we always represent an electric field with an arrow with its tail anchored on the point where the measure- ment is made.
eBook - PDFMatter and Interactions, Volume 2
Electric and Magnetic Interactions
- Ruth W. Chabay, Bruce A. Sherwood(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
C H A P T E R 13 x z y +q –q Electric Field OBJECTIVES After studying this chapter you should be able to Mathematically relate electric field and force. Calculate the 3D electric field at a particular location due to a collection of point charges. Explain the approximations made in deriving expressions for the electric field of a dipole, and use these approximate expressions appropriately. Graphically represent the magnitude and direction of the electric field of a dipole with arrows, at locations in a plane containing the dipole. Create a computational model to compute and display the electric field of a collection of point charges in 3D, and predict the motion of a charged particle that interacts with this field. 13.1 NEW CONCEPTS Two important new ideas will form the core of our study of electric and magnetic interactions. The first is the concept of electric and magnetic fields. This concept is more abstract than the concept of force, which we used extensively in our study of modern mechanics. The reason we want to incorporate the idea of “field” into our models of the world is that this concept turns out to be a very powerful one, which allows us to explain and predict important phenomena that would otherwise be inaccessible to us. The second important idea is a more sophisticated and complex model of matter. In our previous study of mechanics and thermal physics it was usually adequate to model a solid as an array of electrically neutral microscopic masses (atoms) connected by springs (chemical bonds). As we consider electric and magnetic interactions in more depth, we will find that we need to consider the individual charged particles—electrons and nuclei—that make up ordinary matter. The material in this chapter lays the foundation for all succeeding chapters, so it is worth taking time to understand it thoroughly.
- David V. Guerra(Author)
- 2023(Publication Date)
- CRC Press(Publisher)
5 Electric Forces and Fields
DOI: 10.1201/9781003308065-55.1 Introduction
The electric force is another force of nature that is associated with electric charge, which is another property of matter. This chapter begins with a discussion of electric charge and then the format of the electric force is presented and examples are provided. Similar to the previous chapter, the concept of the electric field is discussed along with several examples.- Chapter question: Gel electrophoresis is a lab technique employed to separate and identify biological molecules, based on size. It is used to study proteins and DNA for medical and forensic investigations. The question is, what is the role of the electric field in the lab technique known as gel electrophoresis? This question will be answered at the end of this chapter after the concept of the electric field is developed throughout this chapter.
5.2 Charge
Like mass, charge is a property of matter and it is the starting place for the study of all of electricity and magnetism. Unlike mass that has only one type under normal conditions here on Earth (antimatter is possible but not common), there are two types of charge in common matter that balance each other. These two types are called positive and negative and, in most matter, there are equal amounts of both, so in most objects the net amount of charge is zero. So, it is the imbalance of charge that is measured and referred to in our analysis as charge. It is important to remember that the term charge on an object is not the total charge, but just the imbalance of excess positive or negative charge. The symbol for charge is either a capital or lower case (Q or q). Both symbols are used to represent the imbalance of charge of an object, and it is common to use the upper-case Q for larger charges in a problem and the lower-case q for the smaller charges in a problem. It is also acceptable to use only upper- or lower-case q
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
541 CHAPTER 18 LEARNING OBJECTIVES After reading this module, you should be able to... 18.1 Define electric charge. 18.2 Describe the electric force between charged particles. 18.3 Distinguish between conductors and insulators. 18.4 Explain charging by contact and charging by induction. 18.5 Use Coulomb’s law to calculate the force on a point charge due to other point charges. 18.6 Calculate the net electric field due to a configuration of point charges. 18.7 Draw electric field lines. 18.8 Describe the electric field inside a conductor. 18.9 Use Gauss’ law to obtain the value of the electric field due to charge distributions. We have all experienced static electricity in our hair and on our clothes, and have been zapped on occasion when touching a doorknob after walking on carpet. These phenomena occur when electric charges, one of the fundamental building blocks of atoms, separate, and one type (either positive or negative) becomes more abundant than the other. As we will see in this chapter, like charges repel, which is why the toddler’s hair is standing on end. Rachel Hopper/Dreamstime.com *The definition of the coulomb depends on electric currents and magnetic fields, concepts that will be discussed later. Therefore, we postpone its definition until Section 21.7. Electric Forces and Electric Fields 18.1 The Origin of Electricity The electrical nature of matter is inherent in atomic structure. An atom consists of a small, relatively massive nucleus that contains particles called protons and neutrons. A proton has a mass of 1.673 × 10 −27 kg, and a neutron has a slightly greater mass of 1.675 × 10 −27 kg. Surround- ing the nucleus is a diffuse cloud of orbiting particles called electrons, as Figure 18.1 suggests. An electron has a mass of 9.11 × 10 −31 kg. Like mass, electric charge is an intrinsic property of protons and electrons, and only two types of charge have been discovered, positive and negative.
eBook - ePubHuman Exposure to Electromagnetic Fields
From Extremely Low Frequency (ELF) to Radiofrequency
- Patrick Staebler(Author)
- 2017(Publication Date)
- Wiley-ISTE(Publisher)
1 Concepts of Electromagnetic FieldsElectromagnetic fields are produced from natural and artificial sources. We distinguish between electric, magnetic and electromagnetic fields. Whether static or variable in time, they each have physical properties that produce specific interactions with biological organisms: plant, animal and human.To provide a better understanding of the interaction mechanisms, the concepts of electromagnetism and the associated terminology are presented in this chapter [FEY 15].1.1. Concepts of fields
1.1.1. Introduction
In physics, a field can be defined as an area of influence. We are immersed in the Earth’s gravitational field (the area within which the Earth attracts objects) and in electromagnetic fields (areas within which we can pick up television broadcasts and mobile phone signals, for example).Gravity acts between two bodies that have a mass, while an electric field acts on positive or negative electric charges (electric charge is a fundamental property of matter, along with mass). These interactions are due to forces whose intensity is proportional to the mass of the objects or to the value of the electric charges. They decrease with the square of the distance that separates them and cancel each other out ad infinitum. The expression of these forces is identical. Their intensity in Newton (N) is given, respectively, by the law of gravitation and by Coulomb’s law (in classical physics):- – law of gravitation between two masses m1 and m2 :
[1.1a ]- – Coulomb’s law between two electric charges q1 and q2 :
[1.1b ]where d is the distance in meters between the two objects, G is the universal gravitational constant, and:Coulomb’s constant (N·m2 ·C–2 ), and “c” is the speed of light (≈ 3 × 10+8 m·s–1 ). εois a constant that will be introduced later on. If we refer to the Earth, FG1/2represents the weight and [1.1a] becomes simply P = m·g with g = 9.81 m·s–2
eBook - ePub- L D Landau(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER 3 CHARGES IN ELECTROMAGNETIC FIELDS Publisher Summary This chapter explores charge particles in electromagnetic fields. In the theory of relativity, elementary particles are considered as rigid bodies whose dimensions all remain unchanged in the reference system in which they are at rest. However, it is easy to see that the theory of relativity makes the existence of rigid bodies impossible in general. A charge located in a field not only is subjected to a force exerted by the field, but also in turn acts on the field, changing it. However, if the charge e is not large, the action of the charge on the field can be neglected. The equations of motion of a charge in an electromagnetic field are invariant with respect to a change in sign of the time, that is, the two time directions are equivalent. Thus, if a certain motion is possible according to the equations of mechanics, the reverse motion is also possible, in which the system passes through the same states in reverse order. Furthermore, the gauge invariance of the equations of electrodynamics and the conservation of charge are closely related to one another. The constancy of the acceleration of a charged particle is related to the fact that the electric field does not change for Lorentz transformations having velocities V along the direction of the field. § 15 Elementary particles in the theory of relativity The interaction of particles can be described with the help of the concept of a field of force. Namely, instead of saying that one particle acts on another, we may say that the particle creates a field around itself; a certain force then acts on every other particle located in this field. In classical mechanics, the field is merely a mode of description of the physical phenomenon—the interaction of particles. In the theory of relativity, because of the finite velocity of propagation of interactions, the situation is changed fundamentally
- Nima Gharib, Javad Farrokhi Derakhshandeh, Peter Radziszewski(Authors)
- 2022(Publication Date)
- Elsevier(Publisher)
However, it makes no mention of the test charge Q. The electric field is a vector quantity that varies across points and is governed by the arrangement of source charges as shown in Fig. 3.1 ; physically, E (r) is the force per unit charge that would be exerted on a test charge if placed at P. 4. Continues charge distributions It is worth to emphasize that the electric field, e.g., Eq. (3.4), it is supposed that the field originates from a collection of discrete point charges denoted by q i. Thus, in terms of continues charge distributions, the electric field can be evaluated by the following integral: (3.5) Figure 3.1 Particle location in 3D cartesian system. Figure 3.2 Different types of charge. If the charge is spread along a line with charge/length (see Fig. 3.2B), then, the charge can be evaluated as dq = λdl′. Here, item dl ′ represents a length element along the line. If the charge is smeared across a surface (Fig. 3.2C), then, dq = σda′, where da is an area element on the surface; and if the charge fills a volume (Fig. 3.2D), then dq = ρ dτ ′, where d τ ′ is a volume element. Therefore, the electric field of a line, a surface, and a volume can be formulated as follows, respectively: (3.6) (3.7) (3.8) Eq. (3.8) is sometimes referred to as “Coulomb's law” due to its simplicity in comparison to the original and the fact that a volume charge is the most widespread and realistic situation. Please take notice of the definition of r in the following formulae. Initially, r i denoted the vector between the source charge q i and the field point r in Eq. (3.5). Similarly, in Eqs. (3.6)–(3.8), r denotes the vector connecting dq (and hence dl′, da′, or dτ′) to the field point r. 5. Field lines, flux, and Gauss's law In theory, we have concluded our discussion of electrostatics. Eq. (3.8) demonstrates how to calculate the field of a charge distribution, and Eq. (3.3) demonstrates how to calculate the force acting on a charge Q placed in this field
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