PROBLEMS PROBLEMS 203

Transcription

1 P PROBLMS 203 This time, rather than using meters to make the measurements, we will use indicators. The ndicators key pad is the tenth down on the left toolbar. t has the appearance of an LCD display with the number 8. Once it has been selected, eight possible indicators will appear. For this example, the A indicator, representing an ammeter, will be used since we are interested only in the curent levels. When A has been selected, a Component Browser will appear with four choices under the Component Name List; each option refers to a position for the ammeter. The H means horizontal as shown in the picture window when the dialog box is first opened. The HR means horizontal, but with the polarity reversed. The V is for a vertical configuration with the positive sign at the top, and the VR is the vertical position with the positive sign at the bottom. Simply select the one you want followed by an OK, and your choice will appear in that position on the screen. Click it into position, and you can return for the next indicator. Once all the elements are in place and their values set, simulation can be initiated with the sequence Simulate-Run. The results shown in Fig will appear. Note that all the results appear with the indicator boxes. All are positive results because the ammeters were all entered with a configuration that would result in conventional current entering the positive current. Also note that as was true for inserting the meters, the indicators are placed in series with the branch in which the current is to be measured. PROBLMS SCTON 6.2 Parallel lements 1. For each configuration of Fig. 6.67, determine which elements are in series and which are in parallel (c) FG Problem For the network of Fig. 6.68: a. Which elements are in parallel? b. Which elements are in series? c. Which branches are in parallel? R 4 R 6 R 5 R 7 R 3 FG Problem 2.

2 204 PARALLL CRCUTS P SCTON 6.3 Total Conductance and Resistance 3. Find the total conductance and resistance for the networks of Fig k 2 k 6 k 3.3 k 5.6 k (c) (Standard values) (d) k 40 k (e) (f) (Standard values) FG Problem The total conductance of each network of Fig is specified. Find the value in ohms of the unknown resistances. = 0.55 S 4 R 6 = 0.45 ms 5 k 8 k R FG Problem The total resistance of each circuit of Fig is specified. Find the value in ohms of the unknown resistances. = = 4 9 = 18 FG Problem 5.

3 P PROBLMS 205 *6. Determine the unknown resistors of Fig given the fact that 5 and R 3 (1/2). *7. Determine for the network of Fig = 20 = R 3 24 FG Problem 6. FG Problem 7. SCTON 6.4 Parallel Circuits 8. For the network of Fig. 6.74: a. Find the total conductance and resistance. b. Determine and the current through each parallel branch. c. Verify that the source current equals the sum of the parallel branch currents. d. Find the power dissipated by each resistor, and note whether the power delivered is equal to the power dissipated. e. f the resistors are available with wattage ratings of 1/2, 1, 2, and 50 W, what is the minimum wattage rating for each resistor? 9. Repeat Problem 8 for the network of Fig V 8 k 24 k, FG Problem V 3 6 R FG Problem Repeat Problem 8 for the network of Fig constructed of standard resistor values. 12 V 2.2 k 4.7 k R k, FG Problem 10.

4 206 PARALLL CRCUTS P FG Problem ight holiday lights are connected in parallel as shown in Fig a. f the set is connected to a 120-V source, what is the current through each bulb if each bulb has an internal resistance of 1.8 k? b. Determine the total resistance of the network. c. Find the power delivered to each bulb. d.. f one bulb burns out (that is, the filament opens), what is the effect on the remaining bulbs? e. Compare the parallel arrangement of Fig to the series arrangement of Fig What are the relative advantages and disadvantages of the parallel system compared to the series arrangement? 12. A portion of a residential service to a home is depicted in Fig a. Determine the current through each parallel branch of the network. b. Calculate the current drawn from the 120-V source. Will the 20-A circuit breaker trip? c. What is the total resistance of the network? d. Determine the power supplied by the 120-V source. How does it compare to the total power of the load? Circuit (20 A) breaker 120 V Ten 60-W bulbs in parallel Washer 400-W TV 360-W FG Problems 12 and Determine the currents and for the networks of Fig V 30 V k 1 k 10 k 5 FG Problem 13.

5 P PROBLMS Using the information provided, determine the resistance for the network of Fig *15. Determine the power delivered by the dc battery in Fig A 60 V 12 V FG Problem 14. FG Problem 15. *16. For the network of Fig. 6.82: a. Find the current. b. Calculate the power dissipated by the 4- resistor. c. Find the current V 4 P V FG Problem 16. *17. For the network of Fig. 6.83: a. Find the current. b. Determine the voltage V. c. Calculate the source current. 24 V 2 k V 10 k 4 k FG Problem V

6 208 PARALLL CRCUTS P SCTON 6.5 Kirchhoff s Current Law 18. Find all unknown currents and their directions in the circuits of Fig A 9 A 4 A 6 A 20 A 5 A 8 A 4 A 3 A 9 A R 3 4 A FG Problems 18 and 38. *19. Using Kirchhoff s current law, determine the unknown currents for the networks of Fig ma 6mA 4 ma 2 ma 8 ma 0.5 ma 1.5 ma FG Problem ma 5 ma 2 ma 20. Using the information provided in Fig. 6.86, find the branch resistors and R 3, the total resistance, and the voltage source. 4 k R 3 FG Problem 20.

7 P PROBLMS 209 *21. Find the unknown quantities for the circuits of Fig using the information provided. = 3 A 2 A 2 A 10 V 6 9 R P = 12 W = 100 ma P = 30 W 64 V 1 k R 4 k 30 R 3 = 2 A P R2 (c) (d) FG Problem 21. SCTON 6.6 Current Divider Rule = 6 A 22. Using the information provided in Fig. 6.88, determine the current through each branch using simply the ratio of parallel resistor values. Then determine the total current T. 23. Using the current divider rule, find the unknown currents for the networks of Fig T 4 12 T 2 40 FG Problem A 6 A ma = 4 A (c) (d) FG Problem 23.

8 210 PARALLL CRCUTS P = 10 A k 100 k FG Problem 24. *24. Parts,, and (c) of this problem should be done by inspection that is, mentally. The intent is to obtain a solution without a lengthy series of calculations. For the network of Fig. 6.90: a. What is the approximate value of considering the magnitude of the parallel elements? b. What are the ratios / and /? c. What are the ratios / and /? d. Calculate the current, and compare it to the result of part. e. Determine the current and calculate the ratio /. How does the ratio compare to the result of part (c)? 25. Find the unknown quantities using the information provided for the networks of Fig ma A = 6 ma R 9 FG Problem 25. *26. For the network of Fig. 6.92, calculate the resistor R that will ensure the current 3. *27. Design the network of Fig such that 4 and ma 60 ma 2.2 k 24 V R 3 R FG Problem 26. SCTON 6.7 FG Problem 27. Voltage Sources in Parallel 28. Assuming identical supplies, determine the currents and for the network of Fig Assuming identical supplies, determine the current and resistance R for the parallel network of Fig A 12 V 12 V V R 8 16 V 5 A FG Problem 28. FG Problem 29.

9 P PROBLMS 211 SCTON 6.8 Open and Short Circuits 30. For the network of Fig. 6.96: a. Determine and V L. b. Determine if R L is shorted out. c. Determine V L if R L is replaced by an open circuit V R L 10 k V L FG Problem For the network of Fig. 6.97: a. Determine the open-circuit voltage V L. b. f the 2.2-k resistor is short circuited, what is the new value of V L? c. Determine V L if the 4.7-k resistor is replaced by an open circuit. 2.2 k 3.3 k 9 V 4.7 k V L FG Problem 31. *32. For the network of Fig. 6.98, determine a. the short-circuit currents and. b. the voltages V 1 and V 2. c. the source current V 1 20 V V 2 5 FG Problem 32. SCTON 6.9 Voltmeters: Loading ffect 33. For the network of Fig. 6.99: a. Determine the voltage V 2. b. Determine the reading of a DMM having an internal resistance of 11 M when used to measure V 2. c. Repeat part with a VOM having an ohm/volt rating of 20,000 using the 10-V scale. Compare the results of parts and (c). xplain any difference. d. Repeat part (c) with 100 k and 200 k. e. Based on the above, can you make any general conclusions about the use of a voltmeter? 10 k 6 V 20 k V 2 FG Problems 33 and 40. SCTON 6.10 Troubleshooting Techniques 34. Based on the measurements of Fig , determine whether the network is operating correctly. f not, try to determine why. 3.5 ma 6 V 6 k 3 k 4 k V 6 V FG Problem 34.