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 voltagedivision 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 currentdivision 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 stepby
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 opencircuit 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 shortcircuit 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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 Fall '06
 Preston

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