Voltage constant

Next we consider the second case, where the liquid crystal cell is connected to the voltage source such that the voltage applied V across the cell is fixed. The electric potential in the cell is (z). On top of the cell (z = h), the potential (z = h) = 2 is low. At the bottom of the cell (z = 0), the potential p(z = 0) = tp is high, and 4 i — 4 2= V- The electric field is in the + z direction. The free surface charge density on the top surface of the liquid crystal cell 

There is no free charge inside the liquid crystal, V D = 0, and thus the last term on the right side of the above equation is zero. The surface normal vector points out of the liquid crystal. The first term on the right side of Equation (7.11) becomes 

In a reorientation of the liquid crystal, as discussed in Chapter 1, the change of entropy of the system is given by 

At first glance, it seems that, in order to minimize R, provided Ae 0, n should be perpendicular 

2eo(ei + A Cos 0) So e +A.ecos 6)j where X is the Langrange multiplier. Minimizing Q with respect to we have 

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The growth according to this equation is self-limiting as the field strength F is lowered (at constant voltage) with an increasing film thickness x. 

Some useful expressions can be derived for the variation of the interelectrode gap width, h (Eig. la). If the electrodes constitute a set of plane—parallel electrodes having a constant voltage VappHed across them, and the cathode tool is driven mechanically toward the anode workpiece at a constant rate f, then from Earaday s law the rate of change of gap width h relative to the tool surface is... 

Cold-junction compensation can be provided by a network which includes a constant voltage source and a temperature-sensitive bridge to provide an offset voltage which is proportional to the temperature sensitivity of the thermocouple and of opposite sign. 

The cathode reaction involves reduction of silver oxide to metallic silver [7440-22-4J. The reaction is a two-phase, heterogeneous reaction producing a substantially constant voltage during discharge. Some manganese dioxide may be added to the cathode, as in the case of mercury oxide cells. 

Isoelectric focusing takes along (from ca 3 to 30 h) time to complete because sample compounds move more and more slowly as they approach the pH in the gel that corresponds to their isoelectric points. Because the gradient ampholytes and the samples stop where they have no mobiHty, the resistivity of the system increases dramatically toward the end of the experiment, and the current decreases dramatically. For this reason, isoelectric focusing is usually mn with constant voltage. Constant current appHcation can lead to overheating of the system. 

Use of C is to hold the charge and provide a near constant voltage source to the Inverter... 

Smoothing circuit To obtain a near-constant voltage source for the inverter circuit a smoothing capacitance across the d.c. link is used to smooth the a.c. ripples present in the d.c. link after cotiversion. The capacitor retains the charge and provides a near-constant d.c. voltage output. 

After sjnoothing the d.c. voltage may contain moderate ripples not desirable when a constant voltage d.c. source is needed. To achieve this, a charging capacitor C is also provided across the d.c. link for all sizes of drives as show n in Figures 6.24(a) and 6.28(a). 

Network with linear circuit parameters and constant voltage sources... 

Constant-speed motors are usually suited for a speed range of less than 3 to 1 by field control, but mechanical and electrical characteristics govern maximum safe speeds. With constant voltage on the armature, as the field is weakened the speed increases and the motor develops constant horsepower. 

Notice that the overall reaction does not involve any ions in solution, so there are no concentration changes when current is drawn. As a result, the battery maintains a constant voltage of about 1.3 V throughout its life. 

Figure 4. Discharge characteristics of RAM AA cells when cycled at 20 °C. The cells are discharged for 4 h per day at 4 Q, and charged overnight with a constant voltage charger at 1.7 V.

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