Download Lab EX 3 Series circuit - tech

Exercise 3
Series Circuits
Obiectives
After completing this lab yor-r should be able to:
r
r
r
Discuss the properties of series circuits.
Compute values of voltage, current, and resistance for series circuits.
List rules for solving electrical values of series circuits.
Materials and Equipment
Power supply module
AC voltmeter module
AC ammeter module
EMS BB21
EMS 8426
EMS 8425
Variable-resistancemodule
EMS8311
Ohmmeter (suppliecl by student)
Discussion
A series circuit is a circuit that has only one path for cllrrent florv. Because there is only
one path for cnrrent flow-, the current is the same at ali points in the circuit. There are
three rules thzrt can be usecl with Ohm's law for finding valnes of voltage, curtent, Lesistance, ancl porver in any series circuit. These rules are:
1. The cLlrrent is the same at all points in the circuit.
2. The total resistance is the sum of tl-re resist:rnces of the individual resistors.
3. The applied voltage is equal to the sr-rm of the voltage drops across ali the indi-
viclual resistors.
CONNECTING THE CIRCLIIT
Students often become perplexecl wlien first attemptir-rg to connect an electrical circuit.
Aithough a circuit can appear simple in the fbrm of a schematic diagram, it may become
confusing u'hen an attempt is made to actually connect the circuit. 'fhe rnain reason for
this is that u.hen a circuit is connected it generally bears little resemblance to the
schematic diagram. The circuit shown in Figure 3-1 is a good example. In this circttit,
three resistors are connected in series. A 0.5-A amrneter is connected in the circuit and
a voltmeter with a full scale range of 100 V is connected across each resistor. The entire
circuit is connected to tenninals 4 ancl 5 of the power supply.
17
18 r
E)cRCrsE 3
0.5
R1
Amps
100
Power
supFty
VAC
R3
100 vAc
FIGURE
3-1
Basic series
circuit
The first step nillbe to number the circuit in Figure 3-1. This is clone by starting at
one cnd of the circlrit with the number 1. Each clevice connected to this point will be
Iabelecl 1 also. Each time a clevice is encollntered, the number lvill change. A set of numbers can never be ltsed more than once. In Figure J-2, numlrers have been added to
the circuit shon,n in Figure 3-7. A 1 r'nas placed beside power supply terminal 4 ancl
beside one side of the 0.5-A AC amrneter. Notice that thele is no component between
these two places. The 0.5-A AC meter is a component. When going through a component. the number set mllst change. The other sicle of the ammeter is labeled with the
nunrber 2. There is:rlso a2placecl beside one sicle of the 100-VAC voltmeter 1 (V,) and
one sicle of resistor 1 (R1). The other sicle of voltmeter 1 is labeled v,,ith a 3, the other
side of resistor 1 is labeled with a 3 aiso. One side of voltmeter 2 is labeled with a 3,
and one side of resistor 2 is labeied w-ith a 3. Notice that all these points are electrically
the same. There is no break in tl-ie circuit betrveen any of these components.
Tl"re other sicle of yoltmeter 2 is labeled u,ith a 4r the other side of resistor 2 is labeled
rl ith a 4. One side of voltmeter 3 is labeled rvith a 4. and, one sicle of resistor 3 is labeled
r,vith a 4.
The other side of voltmeter 3 is labeled nith a 5; the other sicle of resistor 3 is
labelecl with a 5, zrnci terminai 5 of the power strpply is 1abelec1 u,ith a 5.
Nou' that the schetnatic has been numberecl, the actnal components that are to
be used in the circttit rvill be labeled with the sarne ntimbers. Figure 3-3 shows the
components that u,i1l be usecl to connect the circtiit. 'l'erminals 4 ancl 5 of the pos,-er
0.5 Anps
100
Poner
suppty
VAC
100 vAc
FIGURE
3-2
Numbers are placed on the schematic.
Series
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ommeten
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te
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Powen
supPty
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34
FIGURE
3-3
Numbers are placed on the components.
supply, the AC ammeter modlrle, the AC voltmeter module, and the variable-resistance
load tnodr:le are sl-iow.n. Notice that numbers have been placed above or below certain terminals on the moclules. A t has been placed beside terminal 4 of the power
supply, ancl above the common terminal of one of the AC ammeters. The schematic
in Figure 3-2 shows ti-rat a 1 l-ras been placeci beside those same two components. A
2 has been placed above the 0.5 terminal of the AC an-rmeter, the common terminal
of voltmeter 1, and one sicle of resistor 1. A 3 has been placed above the 100-V range
terminal of voltmeter 1. belou. the second side of resistor 1, and above the common
terminal of voltmeter 2 and one sicle of resistor 2. Notice tl-rat the schematic ltas zL
3 placed beside the same tenninals.
A 4 has been placed above the 100-V terminal of voltmeter 2, below the second side
of resistor 2, ancl above the common terminal of voltmeter 3 and one side of resistor 3.
Check these nttmbers against the numbers shou,n on the schematic in Figure 3-2.
A 5 has been placecl alrove the 100-V terminal of voltmeter 3, belou., the second side
of resistor 3, ancl at terminal 5 of tl-re power supply. This con-rpletes the nr-rmbering of
the components.
Now tl-rat the components have been numbered to corresponcl w'ith the nr-imbers
on the schematic. the circtrit is connected by connecting all like numbers together. All
the 1s are connected togetl-rer, all the 2s are connected together, all the 3s are connected together, and so on. This numbering system can be r:sed with any schematic
regardless of hor.v involr.ed or complicated it is, if the rr,rles are follow-ed.
Circuits r
t9
Series
Date
Name
Procedure
1. Connect the circuit shown in Figure 3-4.
2. Set the variable resistance moclule so that the resistors in section t have zr total
resistance of 300 fl, the resistors in section 2 hzrve a total resistance of 200 f), and
the resistors in section 3 have a total resistance of 240 Q.
NOTE: Use the chart in Figure 2-2.
J, Compr-rte the value of total resistance
(\)
in the circuit, using the formula
Rr=Rr+R2+R3
Rr:
c)
4. Disconnect the circuit from the polver supply and measure the total resistance of
the circuit with an ohmmeter. Compare this valtre with the computed value.
q:
o
5. Reconnect the circuit to terminals 4 zrnd 5 of the pow"er sr:ppl,v.
6. If an applied voltage of 208 V is assnmecl for this circuit, compllte the total amount
of cr-rrrent flow (Ir) using the fbrmula
_E,
,,r-Rt
Ir=
A
7. Now that t1-re cllrrenf f]on, through the circr-rit is known. the voltage clrop across
each resistor can be computed using the follon'ing fbrmulas
Et=IrxR,
Er:
V
E, = l, xR.,
Ez:
V
Er=IrxR,
E^:
3
0,5 Annp
AC
Power
suPPl,y
FIGURE
34
Each section
of the resistance module
is
connected in series.
Circuits r
21
22 r
E)GRCISE 3
8. Turn on the power supply and adjurst the output voltage for a vaiue of 208 V.
9. Measure the amonnt of current
the computed value.
ir:
10.
flow in the circuit and compzlre this value with
A
Turn off the power supply and connect a 100-VAC voltmeter across the
first section of resistance. This should be the section set for 300 O.
11. Turn on the power supply and measure the voltage drop across this section
of
resistance. Compare this value with the computed value.
Er=
V
off the povrer supply and reconnect the 100-VAC voltmeter across
the second section of resistance.
12. Tutla
13. Turn on the power supply and measure the voltage drop across this section.
Compare this value with the computed value.
Ez:
1,4.
V
Tatrl- off the power supply and reconnect the 100-vAC voltmeter across
tl:e third section of resistance.
15. Turn on the power supply and measure the voltage drop across this section
resistance. Compare this value with the computed value.
E::
of
V
16. Return the voltage
control knob to the zero volt position and turn off the
power supply. Disconnect the circuit and return the components to their
proper place.
Review Questions
1. Define a series circuit.
2. State the three rules for series circuits.
A.
B.
C.
3. A series circuit has resistance values
the total resistance of this circuit?
of
160 C), 100 C), 82
f),
and, 120 Q. \What is
O
4.If a voltage of 24Y
is applied to this circuit. what will be the total amounr of current flow- in the circuit?
5. How much voltage
will be dropped across each of the
760
100
82
720
V
V
V
resistors?