Tab Electronics Guide to Understanding Electricity ... - Sciences Club

Basic Electrical Concepts
75
the remaining 6 volts of the 9-volt source must appear across the two
node connection points. Therefore, there is 6 volts across R1, and the
same 6 volts also appear across the series combination of R2 and R3.
At this point, the current through R2 and R3 can be calculated. Since
they are in series, their resistance values are added:
R total
R 1
R 2
1 Kohm 1 Kohm 2 Kohm
The voltage across the series combination of R2 and R3 was previously
determined to be 6 volts. Therefore, the current flow through them
can be calculated using Eq. (2-2):
E 6 volts
I 3 milliamps or 0.003 amps
R 2 Kohm
(Remember, 2 Kohm 2000 ohms.)
Now that you know the current flow through the R2-R3 leg to be 3
milliamps, you also know that the remaining 7 milliamps (of the total
10-milliamp current flow) must flow through the R1 leg. Since you previously
determined the voltage across R1 to be 6 volts, you now have two
electrical variables relating specifically to R1 from which to calculate its
resistance. Using Eq. (2-3), we have
E 6 volts
R
857 ohms (rounded off from 857.14 ohms)
I 7 milliamps
Of what practical value is this exercise This exercise is primarily
intended to help you understand and develop the concept of conceptualizing
a circuit, regardless of how it happens to be illustrated. Take a few
moments to compare Fig. 2-23c and b, and pay particular attention to
how you can prove both circuits to be electrically identical by following
the current flow path(s) throughout the circuits. It is a common
fault to focus one’s mind on the size, position, or proximity of components
when attempting to analyze a schematic when, in reality, these
factors have little to do with circuit analysis. Until you become more
accomplished at conceptualizing circuits, it is helpful to begin at one of
the source terminals and methodically follow the current flow
through the circuit, paying close attention to connection points, called
nodes, in which the current will divide or sum.
Exercise 13 Referring to Fig. 2-24a, what should the resistance values of
R1 and R2 be It should be relatively obvious that this circuit consists of