document.write( "Question 93127: if z1=2+j, z2=3+j and z3=j3\r
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document.write( "what is the equivalent impedance z if \r
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document.write( "1/z= 1/z1 + 1/z2 + 1/z3 ?? this was a question given to us for homework and it was not in any text book \n" );
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Algebra.Com's Answer #67798 by bucky(2189)![]() ![]() ![]() You can put this solution on YOUR website! You are given three impedances: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "The real part of these impedance is resistance and the imaginary part (called the reactance \n" ); document.write( "and identified as the j terms) are inductances. (You know they are inductances because the \n" ); document.write( "sign of the j terms is plus. If the sign of a j term is negative, then it is a capacitance.) \n" ); document.write( ". \n" ); document.write( "For the first problem you are asked to find \n" ); document.write( "of the three impedances and \n" ); document.write( "three impedances in a circuit and replace them by the equivalent impedance without effect. \n" ); document.write( ". \n" ); document.write( "In finding \n" ); document.write( "adding their real parts and then adding their imaginary parts. Where I listed the three \n" ); document.write( "impedances above, you can just add them in their columns. Adding down the column of real \n" ); document.write( "parts you get 2 + 3 + 0 = 5. And adding down the column of imaginary parts you get \n" ); document.write( "j + j + j3 = +5j. (Note j is the same as j1. So the imaginary parts are j1 + j1 + j3 and \n" ); document.write( "the addition is j(1+1+3) = +j5). \n" ); document.write( ". \n" ); document.write( "So the answer to the first problem is the combination of these two parts, the real part \n" ); document.write( "which is 5 and the imaginary or reactive part which is +j5. Therefore, we say: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "You convert this to polar form just as you would in coordinate geometry. You start at \n" ); document.write( "the origin of an x-y coordinate system and you go +5 units along the x-axis. (That \n" ); document.write( "represents the real part of your answer.) Then from that point (+5 on the x-axis) \n" ); document.write( "you go vertically up (the +j direction) +5 units which represents the imaginary or reactive \n" ); document.write( "part of the answer. [On a graph you are now at the point (5,5).] Now draw a line connecting the \n" ); document.write( "origin with this point (5,5). What you have now is an Argand diagram of the answer, and the \n" ); document.write( "Argand diagram consists of the 5 units along the x-axis, the 5 vertical units from that \n" ); document.write( "point to the point 5,5 and the line connecting the origin to the point (5,5). Just remember \n" ); document.write( "that the real part of the answer (the resistance) is along the x-axis, and the imaginary part \n" ); document.write( "(the vertical) represents the j component of the answer. \n" ); document.write( ". \n" ); document.write( "To find the polar form of the answer you need to look at the Argand diagram and find the \n" ); document.write( "hypotenuse of the right triangle. The hypotenuse will be the magnitude of the answer and \n" ); document.write( "the angle between the x-axis and the hypotenuse will be the polar angle you need. \n" ); document.write( ". \n" ); document.write( "From geometry you may recall that a right triangle that has two legs that are equal in \n" ); document.write( "length is a 45-45-90 degree triangle. Therefore, you know that the angle between the \n" ); document.write( "x-axis and the hypotenuse is 45 degrees. You can use the Pythagorean theorem to find \n" ); document.write( "the length of the hypotenuse (or you could use trig). The Pythagorean theorem tells you to \n" ); document.write( "square each of the legs and add these squares to find the square of the hypotenuse. \n" ); document.write( "So for this problem we have: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "and since \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "To find h just find the square root of 50. You can do it as follows: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Now you know that the magnitude and angle (the polar form) is \n" ); document.write( "at an angle of 45 degrees which is often written as \n" ); document.write( "45 is underlined and is followed by the little \"o\" degrees symbol. (Hard to type the exact \n" ); document.write( "way it is written.) \n" ); document.write( ". \n" ); document.write( "Now for the second part of the problem. A little tougher because of the math manipulations, \n" ); document.write( "but pretty straightforward. \n" ); document.write( ". \n" ); document.write( "The given formula is: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "This is the formula for finding the equivalent impedance of three impedances connected in parallel.\r \n" ); document.write( "\n" ); document.write( "There are several ways this could be done, but let's crank through a straightforward \n" ); document.write( "method. Begin by substituting into the formula the values for the three impedances \n" ); document.write( "to get: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Next recognize that the common denominator on the right side of this equation is: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Let’s multiply this out combine terms. Remember in multiplying that j times j is j squared \n" ); document.write( "and by definition j squared is -1. \n" ); document.write( ". \n" ); document.write( "First let’s begin by multiplying \n" ); document.write( ". \n" ); document.write( "Next multiply that answer times j3: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "If we put all three terms over the common denominator, each term's numerator consists of \n" ); document.write( "the product of the other two terms that were not its denominator. In other words the equation \n" ); document.write( "becomes: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Now let’s multiply out each of the numerators in the three terms. \n" ); document.write( ". \n" ); document.write( "First numerator: \n" ); document.write( ". \n" ); document.write( "Second numerator: \n" ); document.write( ". \n" ); document.write( "Third numerator: \n" ); document.write( ". \n" ); document.write( "Now add all the numerators over the common denominator: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Now we can get the answer for \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Just to make things a little more conventional, let’s factor -1 from both the numerator and \n" ); document.write( "denominator of this answer so that the real portions of answer are positive. This factoring \n" ); document.write( "results in: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "This is not in a useful form yet. We can convert the denominator of this answer by multiplying \n" ); document.write( "it by its conjugate. The conjugate has the same real part and imaginary part, but the imaginary \n" ); document.write( "part has the opposite sign. In this case the denominator is \n" ); document.write( " \n" ); document.write( "the numerator by \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Multiplying the denominator by its conjugate results in: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Then multiplying the numerator by the conjugate of the denominator: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "This further multiplies out to: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Subtracting the two j terms shortens this to: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "The last term involves minus a minus term which is positive: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "The two real parts add and the numerator becomes: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "This gets put over the real denominator which we found to be 401: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Dividing the two terms by 401 results in: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "The Argand diagram will start at the origin and go to the right on the x-axis 0.7855 units. \n" ); document.write( "From that point it will go vertically upward 0.7107 units. You are now at the point \n" ); document.write( "(0.7855, 0.7107). Draw a line from the origin to that point. Again, as in the first \n" ); document.write( "problem, this is the Argand diagram for the equivalent impedance. \n" ); document.write( ". \n" ); document.write( "Next we will use the Argand diagram to find the polar form. The polar form requires that \n" ); document.write( "you have a magnitude and an angle. The magnitude is the length of the hypotenuse in the \n" ); document.write( "Argand diagram, and you can use either the Pythagorean theorem or trig functions to get \n" ); document.write( "the magnitude. This time let’s use trig. We know that the tangent is defined by the side \n" ); document.write( "opposite divided by the adjacent side of the angle. In this problem the side opposite the \n" ); document.write( "angle we are looking for is the vertical side and its length is 0.7107. The adjacent side \n" ); document.write( "is the horizontal side of the triangle and its length is 0.7855. So the tangent of the angle \n" ); document.write( "we are looking for is: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "That means that the angle has a tangent of 0.9048. Using the the tan^(-1) function key \n" ); document.write( "on a calculator we find that the angle with a tangent of 0.9048 is 42.1388 degrees. So \n" ); document.write( "we have half of what we need for the polar form. We still need the hypotenuse and \n" ); document.write( "we can get that using either the sine or cosine function. Let’s use the sine. The \n" ); document.write( "definition of the sine is: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "If we multiply both sides of this equation by the hypotenuse we get: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Then divide both sides by \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "Now we can plug in values. We know the side opposite is 0.7107 and \n" ); document.write( "is the sine of 42.1388 degrees. From a calculator this is 0.6709. So our equation \n" ); document.write( "with these values is: \n" ); document.write( ". \n" ); document.write( " \n" ); document.write( ". \n" ); document.write( "So the polar form of this impedance is 1.0593/42.1388 which is read as 1.0593 ohms at 42.1388 \n" ); document.write( "degrees. \n" ); document.write( ". \n" ); document.write( "Lots of work. Hope this all makes sense to you and you can figure out from this the basics of \n" ); document.write( "finding equivalent impedances for series and parallel circuits. \n" ); document.write( " \n" ); document.write( " |