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206 ⏐⏐⏐ PARALLEL CIRCUITS<br />

FIG. 6.77<br />

Problem 11.<br />

120 V<br />

30 V<br />

I s<br />

Circuit (20 A)<br />

breaker<br />

20 �<br />

5 �<br />

Ten 60-W<br />

bulbs in parallel<br />

I 1<br />

Washer<br />

400-W<br />

FIG. 6.78<br />

Problems 12 and 37.<br />

FIG. 6.79<br />

Problem 13.<br />

11. Eight holiday lights are connected in parallel as shown in<br />

Fig. 6.77.<br />

a. If the set is connected to a 120-V source, what is the<br />

current through each bulb if each bulb has an internal<br />

resistance of 1.8 k�?<br />

b. Determine the total resistance of the network.<br />

c. Find the power delivered to each bulb.<br />

d.. If one bulb burns out (that is, the filament opens),<br />

what is the effect on the remaining bulbs?<br />

e. Compare the parallel arrangement of Fig. 6.77 to the<br />

series arrangement of Fig. 5.87. What are the relative<br />

advantages and disadvantages of the parallel system<br />

compared to the series arrangement?<br />

12. A portion of a residential service to a home is depicted in<br />

Fig. 6.78.<br />

a. Determine the current through each parallel branch of<br />

the network.<br />

b. Calculate the current drawn from the 120-V source.<br />

Will the 20-A circuit breaker trip?<br />

c. What is the total resistance of the network?<br />

d. Determine the power supplied by the 120-V source.<br />

How does it compare to the total power of the load?<br />

(a) (b)<br />

TV<br />

360-W<br />

13. Determine the currents I 1 and I s for the networks of Fig.<br />

6.79.<br />

–8 V<br />

I s<br />

I 1<br />

10 k� 1 k� 10 k�<br />

P

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