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barcode reader in asp.net codeproject We in Software
1 We QR Code 2d Barcode Reader In None Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications. QR Code ISO/IEC18004 Drawer In None Using Barcode creation for Software Control to generate, create QR Code image in Software applications. will use the boldface symbols B and H to denote the vector forms of B and H ; the standard typeface will represent the scalar ux density or eld intensity in a given direction QR Code Decoder In None Using Barcode decoder for Software Control to read, scan read, scan image in Software applications. Creating QR Code ISO/IEC18004 In Visual C# Using Barcode generation for .NET framework Control to generate, create QR Code JIS X 0510 image in Visual Studio .NET applications. Part III
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Generating EAN13 In None Using Barcode creation for Software Control to generate, create UPC  13 image in Software applications. Paint UCC128 In None Using Barcode creator for Software Control to generate, create USS128 image in Software applications. where the symbol denotes the (vector) cross product If the charge is moving at a velocity u in a direction that makes an angle with the magnetic eld, then the magnitude of the force is given by f = quB sin (162) Code 39 Full ASCII Encoder In None Using Barcode printer for Software Control to generate, create Code39 image in Software applications. Generating USS Code 128 In None Using Barcode encoder for Software Control to generate, create Code 128 Code Set B image in Software applications. (161) RM4SCC Drawer In None Using Barcode creation for Software Control to generate, create British Royal Mail 4State Customer Code image in Software applications. Bar Code Scanner In Visual C# Using Barcode Control SDK for .NET Control to generate, create, read, scan barcode image in .NET framework applications. and entering at a magnetic south pole The relative strengths of the magnetic elds generated by two magnets could be depicted as shown in Figure 161 Magnetic elds are generated by electric charge in motion, and their effect is measured by the force they exert on a moving charge As you may recall from previous physics courses, the vector force f exerted on a charge of q moving at velocity u in the presence of a magnetic eld with ux density B is given by the equation EAN128 Maker In Java Using Barcode creation for Java Control to generate, create GS1128 image in Java applications. Generate EAN13 In Visual Studio .NET Using Barcode encoder for Reporting Service Control to generate, create EAN13 image in Reporting Service applications. Weaker magnetic field
Creating UPCA In Java Using Barcode creator for BIRT Control to generate, create UPCA Supplement 5 image in Eclipse BIRT applications. Printing USS Code 128 In ObjectiveC Using Barcode creator for iPhone Control to generate, create Code 128B image in iPhone applications. and the direction of this force is at right angles with the plane formed by the vectors B and u This relationship is depicted in Figure 162 The magnetic ux, , is then de ned as the integral of the ux density over some surface area For the simpli ed (but often useful) case of magnetic ux lines perpendicular to a crosssectional area A, we can see that the ux is given by the following integral: = Encode EAN13 Supplement 5 In ObjectiveC Using Barcode creator for iPad Control to generate, create GTIN  13 image in iPad applications. Recognize USS Code 128 In Java Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications. Stronger magnetic field
Figure 161 Lines of force in a magnetic eld
B dA
(163) f u B
in webers (Wb), where the subscript A indicates that the integral is evaluated over the surface A Furthermore, if the ux were to be uniform over the crosssectional area A (a simpli cation that will be useful), the preceding integral could be approximated by the following expression: =B A (164) Figure 162 Charge moving in a constant magnetic eld
Figure 163 illustrates this idea, by showing hypothetical magnetic ux lines traversing a surface, delimited in the gure by a thin conducting wire Figure 163 Magnetic ux lines crossing a surface
Faraday s law states that if the imaginary surface A were bounded by a conductor for example, the thin wire of Figure 163 then a changing magnetic eld would induce a voltage, and therefore a current, in the conductor More B a b (a) 16
Principles of Electromechanics
a R b Current generating a magnetic flux opposing the increase in flux due to B (b) e + i
Figure 164 Flux direction
i Righthand rule
precisely, Faraday s law states that a timevarying ux causes an induced electromotive force, or emf, e, as follows: d (165) e= dt A little discussion is necessary at this point to explain the meaning of the minus sign in equation 165 Consider the oneturn coil of Figure 164, which forms a circular crosssectional area, in the presence of a magnetic eld with ux density B oriented in a direction perpendicular to the plane of the coil If the magnetic eld, and therefore the ux within the coil, is constant, no voltage will exist across terminals a and b; if, however, the ux were increasing and terminals a and b were connected for example, by means of a resistor, as indicated in Figure 164(b) current would ow in the coil in such a way that the magnetic ux generated by the current would oppose the increasing ux Thus, the ux induced by such a current would be in the direction opposite to that of the original ux density vector, B This principle is known as Lenz s law The reaction ux would then point downward in Figure 164(a), or into the page in Figure 164(b) Now, by virtue of the righthand rule, this reaction ux would induce a current owing clockwise in Figure 164(b), that is, a current that ows out of terminal b and into terminal a The resulting voltage across the hypothetical resistor R would then be negative If, on the other hand, the original ux were decreasing, current would be induced in the coil so as to reestablish the initial ux; but this would mean that the current would have to generate a ux in the upward direction in Figure 164(a) (or out of the page in Figure 164(b)) Thus, the resulting voltage would change sign The polarity of the induced voltage can usually be determined from physical considerations; therefore the minus sign in equation 165 is usually left out We will use this convention throughout the chapter In practical applications, the size of the voltages induced by the changing magnetic eld can be signi cantly increased if the conducting wire is coiled many times around, so as to multiply the area crossed by the magnetic ux lines many times over For an Nturn coil with crosssectional area A, for example, we have the emf d (166) e=N dt Figure 165 shows an N turn coil linking a certain amount of magnetic ux; you can see that if N is very large and the coil is tightly wound (as is usually the case in the construction of practical devices), it is not unreasonable to presume that each turn of the coil links the same ux It is convenient, in practice, to de ne the ux linkage, , as = N so that d dt (167)

