Problem 19.13 Eight bulbs are connected in parallel to a 120 V source by two lon

ID: 1436923 • Letter: P

Question

Problem 19.13

Eight bulbs are connected in parallel to a 120 V source by two long leads of total resistance 1.4 .

Part A

If 250 mA flows through each bulb, what is the resistance of each?

Express your answer to two significant figures and include the appropriate units.

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Part B

If 250 mA flows through each bulb, what fraction of the total power is wasted in the leads?

Express your answer using two significant figures.

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Problem 19.13

Eight bulbs are connected in parallel to a 120 V source by two long leads of total resistance 1.4 .

Part A

If 250 mA flows through each bulb, what is the resistance of each?

Express your answer to two significant figures and include the appropriate units.

R =

SubmitMy AnswersGive Up

Part B

If 250 mA flows through each bulb, what fraction of the total power is wasted in the leads?

Express your answer using two significant figures.

PwastedPtotal =

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let R be the resistance of each bulb

total resistance of 8 bulbs = R/8

equivalent resistance of the circuit = R/8 + 1.4

total current in the circuit I = 250*8 mA = 2 A

from ohms law V = I*Req

120 = 2*(R/8 + 1.4)

R = 468.8 ohms

__________________

power dissipated across leads P1 = I^2*1.4 = 2^2*1.4 = 5.6 W

power dissipated across 8 bulbs P2 = I^2*R/8 = 2^2*468.8/8 = 234.4 W

fraction of power wasted = P1/(P1+P2) = 5.6/(5.6+234.4) = 0.0233