BASIC ELECTRONICS - OD1633 - LESSON 1/TASK 2
(1) Applications of Kirchhoff's Voltage Law.
Kirchhoff's voltage law
can be written as an equation, as shown below:
Ea + Eb + Ec + ...
En = 0
where Ea, Eb, etc., are the voltage drops around any closed circuit loop.
To set up the equation for an actual circuit, the following procedures are
used.
(a) Assume a direction of current through
the
circuit.
(The
correct direction is desirable but not necessary.)
(b) Using the assumed direction of current, assign polarities to
all resistors through which the current flows.
(c) Place the correct polarities on any sources included in the
circuit.
(d) Starting at any point in the circuit, trace around the
circuit, writing down the amount and polarity of the voltage across each
component in succession.
The polarity used is the sign after the assumed
current has passed through the component. Stop when the point at which the
trace was started is reached.
(e) Place these voltages, with their polarities, into the equation
and solve for the desired quantity.
Example: Three resistors are connected across a 50 volt source. What is the
voltage across the third resistor if the voltage drops across the first two
resistors are 25 volts and 15 volts?
Solution: First, a diagram (such as figure 28 on the following page) is
drawn.
Next, a direction of current is assumed (as shown).
Using this
current, the polarity markings are placed at each end of each resistor and
also on the terminals of the source. Starting at point A, trace around the
circuit in the direction of current flow, recording the voltage and polarity
of each component. Starting at point A and using the components from the
circuit:
(+Ex) + (+E2) + (+E1) + (-EA) = 0
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