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4 Ch 2 - l Series resistances have an e equal to their sum...

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Unformatted text preview: l. Series resistances have an e equal to their sum. For n have quivalent resistance resistances in series. we Req=R1+R2+~~+Rn _2. Parallel resistances have an equivalent resistance equal to the reciprocal of the sum of their recipro- cals. For n resistances in parallel, we get 1 R :‘———____ “‘1 1/R1+1/R2 + . - - + we. circuits. Eventually, the currents and voltages of interest in the original circuit are found. 4. The voltage-division principle applies when a volt- age is applied to several resistances in series. A fraction of the total voltage appears across each r sistance. The fraction that a resistance is the ratio of the total series resistance. 6. ppears across a given given resistance to the 5. The current-division principle applies when cur- rent flows through two resistances in parallel. A fraction of the total current flows through each re- sistance. The fraction of the total current flowing through R1 is equal to Rz/(Rl + R2). 6. The node—voltage method can be used to solve for the voltages in any resistive network. A step-by- step summary of the method is given starting on page 72. 7. The mesh- current method can be used to solve for the curre nts in any planar resistive network. A step—by—step summary of the method is given on page 81. '8. A two—terminal network of resistances and sources has a Thévenin equivalent that consists of a voltage source in series with a resistance. The Thévenin . voltage is equal to the open-circuit voltage of Summary 101 the original network. The Thévenin resistance is the open—circuit voltage divided by the short- circuit current of the original network. Sometimes, the Thévenin resistance can be found by zeroing the independent sources in the original network and combining resistances in series and parallel. When independent voltage sources are zeroed. they are replaced by short circuits. Independent current sources are replaced by open circuits. De- pendent sources must not be zeroed. has a Norton equivalent that consists of a cur- rent source in parallel with a resistance. The Nor— ton current is equal to the short-circuit current of the original network. The Norton resistance is the same as the Thévenin resistance. 10. The superposition principle states that the total response in a resistive circuit is the sum of the re- sponses to each of the independent sources acting individually. The superposition principle does not apply to any circuit that has element(s) described by nonlinear equation(s). 11. The Wheatstone bridge is a circuit used to mea- sure unknown resistances. The circuit consists of a voltage source, a detector. three precision cali- brated resistors. of which two are adjustable, and the unknown resistance. The resistors are adjusted until the bridge is balanced. and then the unknown resistance is given in terms of the three known re- sistances. Here‘s the answer to the trick question on page 90: Suppose that we open circuit the termi- their terminal voltage and current their internal behavior. ...
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