Electric current work done

A calorimeter is a device used to measure the work that would have to be done under adiabatic conditions to bring about a change from state 1 to state 2 for which we wish to measure AU= U -U This work is generally done by passing a known constant electric current 3 for a known time t through a known resistance R embedded in the calorimeter, and is denoted by where... 

Other methods attempt to probe the stmcture of the foam indirectly, without directly imaging it. Eor example, since the Hquid portion of the foam typically contains electrolytes, it conducts electrical current, and much work has been done on relating the electrical conductivity of a foam to its Hquid content, both experimentally (15) and theoretically (16). The value of the conductivity depends in a very complex fashion on not only the Hquid content and its distribution between films and borders, but the geometrical stmcture of the bubble packing arrangement. Thus electrical measurements offer only a rather cmde probe of the gas Hquid ratio, a quantity that can be accurately estimated from the foam s mass density. 

The work done by an electric motor when electric current passes through its coils. 

Figure 7-5 shows an apparatus in which an electric current can be passed through water. As remarked in Section 3-1.2, the electric current causes a decomposition of water. As work is done (electrical work), hydrogen gas and oxygen gas are produced. Measurements of the electric current and voltage show that 68.3 kcal of electrical work, W, must be done to decompose one mole of water. The equation for the reaction is... 

An extruder is a complicated device to control. Often the barrel is divided into three sections, and the temperature at the exit of each section determines the additional amount of electrical energy to be supplied. Most of the energy for heating is provided by the screw. The throughput is usually set by the rate at which the screw rotates, and is maintained constant. Work is currently being done on the effect of extruder operating conditions on product quality. Preliminary conclusions indicate that conditions should be kept as constant as possible if reproducible results are desired. 

In this chapter, we will deal with experiments that measure electric potentials and currents. Electric potential is measured in volts (V), electric charge in coulombs (C), and electric current in amperes (1 A = 1 C/s). Electrical work is done when a charge Q is passed through a potential difference, AV, with 1 J = 1 V C,... 

In equation (16-1), q is the heat absorbed from the surroundings and w is the work done on the system. A few examples of work are (1) if a chemical reaction occurs within a system, work may be done upon it if gases are consumed and its volume is decreased, or (2) the system may perform work if gases are produced, or (3) work may be done if the system delivers an electric current to an external circuit. 

If the two plates are connected by a wire there will be a current. through the wire. Let us suppose that there are 200 cells in the battery so that the P.D. between the plates is 300 volts or one electrostatic unit of P.D. If the current in the wire is one ampere this means that 3,000,000,000 electrostatic units of electricity flow from one plate to the other in one second. The work done on the electricity in one second will then be 3,000,000,000 ergs because when the P.D. is one electrostatic unit of P.D. the work required to take one electrostatic unit of charge across is one erg. 

If the P.D. was only one volt instead of 300 volts the work done on the electricity when a current of one ampere was flowing through the wire would be 300 times smaller or 10,000,000 ergs per second. This work or energy appears as heat in the wire, which gets hot. 

Work done on or by a closed system is accomplished by movement of the system boundary against a resisting force or the passage of an electrical current or radiation across the system boundary. Examples of the first type of work are motion of a piston or rotation of a shaft that projects through the syste nr boundary. If there are no moving parts or electrical currents or radiation at the system boundary, then W = 0. 

The minus sign appears in this equation because the same thermodynamic convention is followed as in Chapters 12 and 13—that work done by the system (here, an electrochemical cell) has a negative sign. Because work is measured in joules and charge in coulombs, has units of joules per coulomb. One volt (abbreviated V) is 1 joule per coulomb. Because the total charge Q is the current / multiplied by the time t in seconds during which the current is flowing, this equation for the electrical work can also be written... 

A 6.00-V battery delivers a steady current of 1.25 A for a period of 1.50 hours. Calculate the total charge Q, in coulombs, that passes through the circuit and the electrical work done by the battery. 

In general, the work that can be obtained in an isothermal change is a maximum when the process is performed in a reversible manner. This is true, for example, in the production of electrical work by means of a voltaic cell. Cells of this type can be made to operate isothermally and reversibly by withdrawing current extremely slowly ( 331) the e.m.f. of a given cell then has virtually its maximum value. On the other hand, if large currents are taken from the cell, so that it functions in an irreversible manner, the E.M.F. is less. Since the electrical work done by the cell is equal to the product of the e.m.f. and the quantity of electricity passing, it is clear that the same extent of chemical reaction in the cell will yield more work in the reversible than in the irreversible operation. 

This maximum work is obtained if the process is sufficiently slow that there are no irreversibilities, for example, no resistive heating as a result of the current flow. This implies that the rate of reaction is very slow, and that the electrical potential produced is just balanced by an external potential so that the current flow is infinitesimal. This electrical potential produced by the cell (or of the balancing external potential) will.be referred-to as-the zero-current cell potential and designated by E. The work done by... 

The question of the work done on chemical systems must also be considered. There are various ways in which a system may do work, or by which work may be done on a system. For example, if we pass a current through a solution and electrolyze it we perform one form of work—electrical work. Conversely, an electrochemical cell performs work, as will be considered in detail in Chapter 8. Living systems also perform work and this work can be classified into three basic types chemical work, osmotic work, and inechanical work. Chemical work is done by all biological ceils, not only... 

It would appear that the technique shows promise but more work needs to be done on the use of magnetic devices for the reduction of scaling problems before the technology can be used with confidence. Furthermore the possibility of inducing electric currents in metallic structures, that could result in enhanced corrosion (see Chapter 10), must be carefully considered. 

Scanning tiiniiclling microscopy (STM) works in a rather similar way to AFM, but the surface is detected by measuring the very weak electric current that flows (by electron tunnelling) between the sample and the tip when they are very close together with a voltage between them. Unlike AFM, this cannot be done under water. 

Faraday had worked out the laws of electrolysis, and from those laws it had seemed that electricity, like matter, might well exist in the form of tiny particles (see page 90). Faraday had spoken of ions, which might be considered as particles carrying electricity through a solution. For the next half century, however, neither he nor anyone else had ventured to work seriously on what the nature of those ions might be. This did not mean, however, that no valuable work was done. In 1853, the German physicist Johann Wilhelm Hittorf (1824-1914) pointed out that some ions traveled more rapidly than others. This observation led to the concept of transport number, the rate at which particular ions carried the electric current. But even calculation of this rate still left the nature of ions an open question. 

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