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Unformatted text preview: Chapter 1 Direct Current Circuits l9 Ri
A Voltage Sources
B Current Sources FIGURE 1.24 Voltage and current sources. ideal current source has an inﬁnite Norton resistance. The ideal and real cur—
rent sources are symbolized in Figure 1. 24B. In later chapters, time-varying
voltage and current sources will be encountered As long as their outputs are
unaffected by the circuit load, they are ideal The mercury battery closely approximates an ideal voltage source when
used correctly, in that the battery voltage remains constant. A simple constant
current source can be constructed with a battery and a very large resistance
in series with it. Within limits, the current is constant as long as the load
resistance does not approach that of the constant current resistance. 1-14 QUESTIONS AND PROBLEMS 1. What is the resistance of a carbon rod which is 1 cm
in diameter and 10 cm long? 2. A nichrome wire, 1 mm in diameter and 1 meter long,
has what resistance? 3. What is the maximum allowable current through a
10 k0, 10 W resistor? Through a 10 k0, 1/4 W resistor? 4. What wattage rating is needed for a 100 0 resistor if . . /
FI RE A t f
100 V is to be applied to it? For a 100 k0 resistor? GU Clrcul or problems 5 and 6‘ 5. Compute the current through R3 of Figure A.
measured with voltrneters whose effective resistances are 100 (I, 1 k0, 50 1(5), and 1 MD. What voltage will each
7. The output of the voltage divider of Figure B is to be indicate? 6. Compute the currents through R1 and R2 of Figure A. 20 Chapter 1 Direct Current Circuits 2k9 3V 1k9 v out 1 FIGURE B Circuit for problem 7. 8. The internal resistance of a 1.5 V zinc—carbon battery
is found to be 1.5 9. What is the maximum current available? 9. A 12 V storage battery is rated at 70 A. What is its
internal resistance? 10. A voltmeter whose resistance is 1000 9 measures the
voltage of a worn-out 1.5 V ﬂashlight battery as 0.9 V. What
is the internal resistance of the battery? 11. If the ﬂashlight battery of the preceding problem had
been measured with a voltmeter with a resistance of 10 M9,
what voltage would have been read? 12. What is the effective resistance of the circuit in
Figure C? ‘ 13. Suppose that a 25 V battery had been applied to the
terminals of the circuit in Figure C. Calculate the current in the 10 9 resistor. 39
59 2 9
FIGURE C Circuit for problems 12 and 13. 14. Derive the conditions of balance for the Wheatstone
bridge. 15. Compute the current through R2 of the circuit in Fig—
ure D. 16. Using the following values for the circuit in Figure D,
compute the current through R3. V2=15V FIGURE D Circuit for problems 15, 16, and 17. VI = 1.500v V2 = 1.082V 1e1 =27879 R2=72139 R3: 109 17. Using the values of the preceding problem, compute
the current through R2. Also compute the current through R2 when R3 = 10 k9. 18. Using Thévenin’s theorem, determine the effective
voltage and the effective resistance of the circuit in Figure B
with V2 removed. FIGURE E Circuit for problem 18. 19. Using Thévenin’s theorem. determine the effective
voltage and the effective resistance of the circuit in Figure F with R5 removed. R1=IOO9
V= 10V FIGURE F Circuit for problems 19, 20, 21 and 22. 20. What is the current through R5 of the circuit of
Figure F? ' 21.
wot 22. inP 23.
3 9 24.
cuit 1 26. 27.
Thév‘ Chapter 1 Direct Current Circuits 21 resistor is removed. Verify the equivalence of these circuits
by comparing the current through the 10 Q resistor in each
case. 21. If R5 = 10 k0 instead of 10 D. in Figure F, what
would be the current through it? 22. Calculate the voltage across R5 for the conditions cited
in Problems 20 and 21. 23. In the circuit of Figure G, compute the current in the 3 .Q resistor and ﬁnd the value of V2. V1=5 V
Rﬁ=3o 0.833 A 1.389 A
—> 4— 49 69 10v 39 v2 FIGURE J Circuit for problem 26.
FIGURE G Circuit for problem 23. 24. In the circuit of Figure H, ﬁnd the value of V3 such
that the current through the 10 .Q resistor is zero. 12 a; 99 69 109
30V 15V V3 FIGURE H Circuit for problem 24.
FIGURE K Circuit for problem 27. 25. Compute the current in each of the resistors in the cir- cuit of Figure I. 28. Write the appropriate equations for the three currents designated in Figure L. 4.0 9 4.0 V FIGURE I Circuit for problem 25. F1 ' 't b .
26. Compute the currents labeled in the circuit of Figure I. GURE L Circul for pro lems 28 and 29 27. Compute the current through the 10 Q resistor in the 29. Calculate the current through R3 of the circuit in Fig- circuit of Figure K. Also compute the Thévenin voltage, the
Thévenin resistance, and the Norton current when the 10 Q ureLwhenV1= 5V,V2 =lOV,R1= 209,R2 = 400,
andR3=2Q _ ...
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