Electrical work in a circuit

Electric current is usually conducted in an electrical circuit. Consider a thermod5mamic system that is part of a circuit in a given time period electrons enter the system through one wire, and an equal number of electrons leave through a second wire. To simplify the description, the wires are called the right conductor and the left conductor. 

The sum of charges of a small number of electrons can be treated as an infinitesimal negative charge. During a period of time in which an infinitesimal charge dtgsys enters 

What is the meaning of gsys in the differential dgsys We define gsys as the total cumulative charge, positive or negative, that has entered the system at the right conductor 

The electric current I is the rate at which charges pass a point in the circuit I = d 3sys/dt, where t is time. We take I as negative if electrons enter at the right conductor and positive if electrons leave there. This relation provides an alternative form of Eq. 3.8.1  

Equations 3.8.1 and 3.8.3 are general equations for electrical work in a system that is part of a circuit. The electric potential difference A which appears in these equations may have its source in the surroundings, as for electrical heating with a resistor discussed in the next section, or in the system, as in the case of a galvanic cell (Sec. 3.8.3). 

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Electrical work in a circuit dm — A0 d(2sys A0 = electric potential difference d sys = charge entering system at right... 

A schematic diagram is a diagram in outline of, for example, a motor starter circuit. It uses graphical symbols to indicate the interrelationship of the electrical elements in a circuit. These help us to understand the working operation of the circuit but are not helpful in showing us how to wire the components. 

Capacitance or conductance measurement This method is applied where the working fluid acts as a capacitive or conductive element in a circuit (Jones et al., 1981). Use of fiber optics sensors has been developed recently (Moujaes and Dougall, 1987, 1990). These methods are used to measure film thickness in annular flow. Further discussion appears in Section 3.3.4.4. For other regimes, the use of the electrical impedience imaging method has also been introduced (Lin et al., 1991). 

The term voltammetiy may be contrasted with a term such as potentiometiy. Of course, the use of volt comes from Volta, who in 1800 reported die first electric battery. In a similar way. one refers to amps as a measurement of current because of the very early work of Ampere on electrical circuits. The trend now is to use the generic term (potential, current) instead of the historical one (volt, ampere). 

In an electrical system, if the power factor is 0.80, 80% of the apparent power is converted into useful work. Apparent power is what the transformer that serves a home or business has to carry in order for that home or business to function. Active power is the portion of the apparent power that performs useful work and supplies losses in the electrical equipment that are associated with doing the work. Higher power factor leads to more optimum use of electrical current in a facility. Can a power factor reach 100% In theory it can, but in practice it cannot without some form of power factor correction device. The reason why it can approach 100% power factor but not quite reach it is because all electrical circuits have inductance and capacitance, which introduce reactive power requirements. The reactive power is that... 

The electrochemical processes occurring in this cell are the oxidation of zinc and the production of zinc sulfate and electrons at the anode, the absorption of electrons an the reduction and deposition of copper at the cathode, the flow of electrons through an external electrical circuit (resulting in electrical work), and a balancing flow of sulfate ions through the salt bridge. 

Wet or damp environments Water can be a good conductor of electricity, hence working with electrical equipment in a wet environment can be a hazardous activity. Electrical equipment should be isolated from moisture. Electrical receptacles in wet or damp environments must be designed for this type of environment, with ground-fault-circuit-interrupter (GFCI) protection. This type of receptacle should be tested periodically in accordance with the manufacturer s recommendations. 

Isolation is defined as cutting off the electrical supply to a circuit or item of equipment in order to ensure the safety of those working on the equipment by making dead those parts whioh are live in normal service,... 

In a typical fuel cell, there are two electrodes, an anode from which electrons are removed during the oxidation of hydrogen, a cathode to which electrons flow during the reduction of oxygen, an ion-conducting electrolyte which electrochemically connects the anode and cathode, and an external circuit through which the electrons flow from the anode to the cathode while doing electrical work. In early fuel cells. 

The electrical work performed on this system is given by the expressions dWei = Acp dgsys and dwei = IA

electrical circuit inside the system has an electric resistance given by Re = A(p/1 (Ohm s law). Making the substitution Acp = I Re in the work expressions gives two new expressions for electrical work in this system ... 

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