Physics
Electric Cells
Electric cells are devices that convert chemical energy into electrical energy. They consist of two electrodes (anode and cathode) and an electrolyte. When the electrodes are connected by a conductor, a chemical reaction occurs, generating a flow of electrons and creating an electric current. Electric cells are used in batteries to power various electronic devices.
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8 Key excerpts on "Electric Cells"
eBook - PDFIndustrial Electronics N1 Student's Book
TVET FIRST
- M Gobind RBJ van Heerden(Author)
- 2020(Publication Date)
- Troupant(Publisher)
The difference between a cell and a battery A cell is a single unit that produces electricity through a chemical reaction, whereas a battery is a combination of cells used to increase either the voltage or the current, depending on the required application. Cells can be connected to one another either in series or in parallel in order to form a battery (see Figure 2.2). Cells that are connected in series increase the electromotive force (emf) , while those connected in parallel increase the available current. (a) (b) (c) (d) Figure 2.2: Circuit symbols for (a) a cell, (b) a battery, (c) cells connected in a series/parallel arrangement and (d) cells connected in a parallel arrangement Unit 2.1: Primary cells A primary cell can be defined as a device that can produce or generate an electrical potential (electrical pressure or voltage) that can deliver an electric current for as long as the chemical reaction used in the process is active. This cell cannot be recharged. Primary cells are most commonly used as a portable non-rechargeable source of direct-current power. 2.1.1 Construction and operation The chemical action that takes place in primary cells is a very complicated process and beyond the scope of this book. However, you will require some basic knowledge of it to understand the operation of chemical cells in general. primary cell: a cell that produces current by an irreversible chemical reaction and cannot be recharged rechargeable: can be charged repeatedly (more than once) secondary cell: a cell that produces current by a reversible chemical reaction and can be recharged many times voltage: electrical pressure, expressed in volt (V); an electromotive force (emf) or potential difference (pd) electromotive force (emf): a difference in potential between the positive and negative terminals of a cell or battery measured in volt (V); also referred to as open-circuit voltage (electrical pressure), where no current flows in the external circuit
- Dale Crane, Dennis Wilt(Authors)
- 2017(Publication Date)
- Aviation Supplies & Academics, Inc.(Publisher)
6 Chemical Energy Into Electricityelectrochemical cell . A device in which a chemical reaction produces electrical energy.One of the more important devices used to produce electricity is the battery, or more accurately, the electrochemical cell.All of nature is composed of atoms, which consist of a nucleus containing positive protons and neutral neutrons. Spinning around this nucleus in shells, or rings, are negatively charged particles of electricity, called electrons. When atoms of some of the chemical elements react with atoms of other elements, electrons are released from one element, and they are attracted to the other. The force of attraction for these electrons is an electrical pressure called voltage.Simple Chemical Cell The way chemical energy is changed into electrical energy may be seen by studying the simple electrochemical cell in Figure 6-1.A strip of zinc and a strip of copper placed in a solution of hydrochloric acid and water form an electrochemical cell.Figure 6-1 . In a simple electrochemical cell, the zinc reacts with chlorine ions from the hydrochloric acid to form zinc chloride. This reaction causes the zinc to release electrons, which travel through the external circuit to the copper, where they attract and neutralize hydrogen ions from the hydrochloric acid.Two atoms of hydrogen make one molecule of hydrogen gas, which forms as bubbles on the copper.The electrolyte (the acid and the water) contains positive hydrogen ions and negative chlorine ions. Zinc is an active chemical element, and it reacts, or combines, with the chlorine to form zinc chloride. When negative chlorine ions from the electrolyte combine with the zinc, the zinc becomes negative; the ions have given it an excess of electrons.If a conductor joins the zinc and the copper, the excess electrons will leave the zinc and travel through the conductor to the copper, where they attract positive hydrogen ions from the electrolyte. Hydrogen ions accept the electrons and become neutralized and two hydrogen ions combine to form molecules of hydrogen gas (H2
eBook - PDFBatteries for Electric Vehicles
Materials and Electrochemistry
- Helena Berg(Author)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
I Electrochemistry and battery technologies 1 The electrochemical cell The most fundamental unit of a battery is the electrochemical cell. All performance characteristics are dependent on the materials inside the cell, and all cells work according to some general principles independent of the materials employed. The purpose of this chapter is to bring together the fundamental aspects of an electrochemical cell as the basis for all further steps in the development of a battery intended for electric vehicles. An electrochemical cell converts chemical energy to electric energy when discharged, and vice versa. In addition, the electrochemical cells can be said to be either electrolytic or galvanic. In an electrolytic cell, the electric energy is converted to chemical energy (charging of the battery) and in a galvanic cell chemical energy is converted to electric energy (discharging of the battery). The basic design of an electrochemical cell consists of a positive and a negative electrode separated by an electrolyte, as shown in Figure 1.1. The chemical reactions taking place during charge and discharge processes are based on electrochemical oxidation and reduction reactions, known as the redox reactions, at the two electrodes. In these reactions, electrons are transferred via an external circuit from one electrode to another, and at the same time ions are transferred inside the cell, through the electrolyte, to maintain the charge balance. The species oxidised is called the oxidant, and the species reduced is called the reductant. The oxidation reaction takes place at the negative electrode, the anode, and electrons are transferred, via the external circuit, to the positive electrode, the cathode, where the reduction reaction takes place by accepting the electrons. The negative electrode is thus an electron donor, and the positive electrode an electron acceptor. During charge and discharge of a battery, the nomenclature of the electrodes changes.
- Bent Sorensen, Bent Sørensen(Authors)
- 2007(Publication Date)
- Academic Press(Publisher)
BENT SØRENSEN 168 V. E LECTROCHEMICAL ENERGY CONVERSION PROCESSES PEM FUEL CELL - BENT SØRENSEN, 2002 19. FUEL CELLS V. ELECTROCHEMICAL ENERGY CONVERSION 169 F UEL CELLS 19.1 Electrochemical conversion Electrochemical energy conversion is the direct conversion of chemical en-ergy, i.e. free energy of the form (2.8) into electrical power or vice versa . A device that converts chemical energy into electric energy is called a fuel cell (if the free energy-containing substance is stored within the device rather than flowing into the device, the name “primary battery” is sometimes used). A device that accomplishes the inverse conversion (e.g. electrolysis of water into hydrogen and oxygen) may be called a driven cell. The energy input for a driven cell need not be electricity, but could be solar radiation, for example, in which case the process would be photochemical rather than electrochemical. If the same device is used for conversion in both directions, or if the free energy-containing substance is regenerated outside the cell (energy addition required) and recycled through the cell, it may be called a regenerative or reversible fuel cell and, if the free energy-containing substance is stored inside the device, a regenerative or secondary battery. All fuel cell types are in principle capable of operation in both directions, although a particular cell may have been optimised for a particular process. The basic ingredients of an electrochemical device are two electrodes (sometimes called anode and cathode) and an intermediate electrolyte layer capable of transferring positive ions from the negative to the positive elec-trode (or negative ions in the opposite direction), while a corresponding flow of electrons in an external circuit from the negative to the positive elec-trode provides the desired power.
eBook - PDF- Keith Oldham, Jan Myland(Authors)
- 2012(Publication Date)
- Academic Press(Publisher)
3 Electrochemical Cells In Chapter 1 the two classes of conductor - electronic and ionic - were discussed. It is at the junction between an electronic conductor and an ionic conductor (we call such a junction an electrode) that the chemistry of electrochemistry occurs. Economically important examples of such chemistry are discussed in the later sections of this chapter. 3:1 Cell voltages and currents The simplest electrochemical unit consists of an ionic conductor sandwiched between two electronic conductors. One may think of this as an aqueous solution of electrolytes between two pieces of metal - and this is often the case - but the sandwich combination of any ionic conductor and any pair of (similar or dissimilar) electronic conductors constitutes an electrochemical cell. electronic 1 electronic conductor ionic j conductor conductor Î electrode electrode In order to make measurements on the cell one needs at least a voltmeter attached to the cell. As discussed in Section 1:2, this device measures the electrical potential difference between the two electronic conductors. If the black lead of our voltmeter is connected to the right-hand electronic 63 3 Electrochemical Cells conductor, as diagrammed above, and the red lead to the left, then the voltmeter is said to measure the electrical potential difference of the left-hand electronic conductor with respect to the right. This measured potential difference may be positive, negative or zero and will be denoted AE. It is often simply called the cell voltage*. Let us consider, as a specific example, the electrochemical cell that is familiar to most people: the lead/acid cell. Six such cells make up the common car battery. One of the electronic conductors of the lead/acid cell is essentially lead dioxide, P b 0 2 ; the other is lead, Pb. The ionic conductor^ is a concentrated aqueous solution of sulfuric acid. At the concentration used in battery acid, H 2 S 0 4 is entirely ionized to H + and HSO4 ions.
eBook - PDF- G. G. Járos, B. J. Meyer(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
principles as the Voltaic cell, but which make use of other chemicals and metals. In all of them the EMF is determined by the chemical reactions. In Table 5.1 the different types of cells with their electromotive forces are shown. Production of Electricity 5: 3 Type of cell Voltaic Daniell Weston Clark Edison Leclanch£ Mercury Nickel-cadmium Electromotive force {volt) 1,06 1,09 1,18 1,43 1,5 1,5 1,42 1,22 TABLE 5.1 The electromotive force produced by different cells. When two or more cells are connected in series they form a battery. The EMF of a battery is the sum of the EMF of the individual cells. For example a battery that consists of 6 cells each having an EMF of 1,5 volt, has an EMF of 6 x 1,5 = 9 volts. Usually the cells of a battery are enclosed in a container and the whole battery is provided with two terminals. The symbols used to indicate cells and batteries are shown in FIG. 5.2. *) 11 b) —ΜΗΗΨ— c) — | i |i FIG. 5.2 Schematic representation of (a) a single cell — the longer vertical line indicates the positive pole of the cell; (b) and (c) cells connected in series to form a battery. A battery with cells which can be recharged after they have stopped producing electromotive force, is called an accumulator. A good example of an accumulator is the battery of a car. During the charging process, a current is sent through the battery in the opposite direction to normal flow. This causes the regeneration of the original chemical compounds and the battery can be used again. The amount of electricity that can be produced by a cell (capacity) is determined by the amount of chemicals available in the cell and 5:4 Electrkity is thus constant for a given cell. When current flows between the electrodes of a battery, the charge difference tends to disappear, but chemical reactions proceed which keep the EMF constant. The available chemicals are therefore used, and the greater the current, the greater the ion consumption will be and the shorter the life of the cell.
eBook - PDF- Edward Purcell(Author)
- 2011(Publication Date)
- Cambridge University Press(Publisher)
That is, a positive charge carrier may move to a place of higher electric potential if by so doing it can engage in a chemical reaction that will yield more energy than it costs to climb the electrical hill. To see how this works, let us examine one particular voltaic cell. Voltaic cell is the generic name for a chemical source of electromotive force. In the experiments of Galvani around 1790 the famous twitch- ing frogs' legs had signaled the chemical production of electric cur- rent. It was Volta who proved that the source was not "animal elec- tricity," as Galvani maintained, but the contact of dissimilar metals in the circuit. Volta went on to construct the first battery, a stack of elementary cells, each of which consisted of a zinc disk and a silver disk separated by cardboard moistened with brine. The battery that powers your transistor radio comes in a tidier package, but the prin- ciple of operation is the same. Several kinds of voltaic cells are in use, differing in their chemistry but having common features: two elec- ELECTRIC CURRENTS trodes of different material immersed in an ionized fluid, or electrolyte. As an example, we'll describe the lead-sulfuric acid cell which is the basic element of the automobile battery. This cell has the impor- tant property that its operation is readily reversible. With a storage battery made of such cells, which can be charged and discharged repeatedly, energy can be stored and recovered electrically. A fully charged lead-sulfuric acid cell has positive plates which hold lead dioxide, Pb0 2 , as a porous powder, and negative plates which hold pure lead of a spongy texture. The mechanical framework, or grid, is made of a lead alloy. All the positive plates are connected together and to the positive terminal of the cell. The negative plates, likewise connected, are interleaved with the positive plates, with a small separation. The schematic diagram in Fig. 4.20 shows only a small portion of a positive and a negative plate.
eBook - PDF- John Matolyak, Ajawad Haija(Authors)
- 2013(Publication Date)
- CRC Press(Publisher)
275 © 2010 Taylor & Francis Group, LLC Direct Current Circuits 15.1 INTRODUCTION Electric circuits are an excellent example of employing the properties of electric charges, covered in Chapters 13 and 14, for practical purposes. Circuits generally consist of (1) a source of charge, for example, a battery or an electric generator, (2) a conducting path for charge and hence energy flow, (3) a “load,” that is, a charge/energy consuming device such as a radio, light bulb, and electric motor. 15.1.1 C ELLS AND B ATTERIES AS A S OURCE OF C HARGE A simple chemical cell can be constructed by placing two dissimilar metals, say A and B, in a dilute acid. As an example, the metals (electrodes), generally in the shape of rods, could be copper and zinc. Most metals dissociate (dissolve) slightly in the acid. The dissociation results in a positive ion being removed from the metal and entering the acid solution. That metal ion leaves behind at least one electron and therefore negatively charges the rod from which it came. Over time, as the process continues, the rod becomes negative enough to attract some of the positive ions in solution back to it. Eventually, an equilibrium is reached so that the number of positive ions leaving the rod equals the number attracted back to it. The electrode now is negatively charged, so a potential difference exists between it and the solution, which is at a higher potential. A similar process occurs with rod B and it likewise reaches an ion dissociation–attraction equilibrium. But metal B is dissimilar to electrode A and suppose it is more electronegative, that is, retains more electrons per dissociation than A. Both A and B are negative, so they are at a lower potential than the solution, but because of its greater electron retention, B is at a lower potential than A. This potential difference is tradition-ally called the electromotive force (a misnomer) or emf of the cell.
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