Three 30.0-W, 135-V lightbulbs are connected across a ? V = 135-V power source,

Question

Three 30.0-W, 135-V lightbulbs are connected across a ?V = 135-V power source, as shown in the figure below. Find the total power delivered to the three bulbs and the potential difference across each. Assume the resistance of each bulb is constant (even though, in reality, the resistance increases markedly with current).

?VR1 = V ?VR2 = V ?VR3 = V Three 30.0-W, 135-V lightbulbs are connected across a ?V = 135-V power source, as shown in the figure below. Find the total power delivered to the three bulbs and the potential difference across each. Assume the resistance of each bulb is constant (even though, in reality, the resistance increases markedly with current). (a) Find the total power delivered to the three bulbs. Your response differs from the correct answer by more than 100%. W (b) Find the potential difference across each bulb.

Explanation / Answer

P = V^2/R

R= V^2 / P = (135)^2 / 30 = 607.5 ohm

Req = R/2 + R = 3R/2 = 911.25 ohm

I = 135 / 911.25 =.148 A

Ptotal = V*I = 135 *.148 =20 W

b) Vr1 = I*R = 89.91 V

Vr2 = Vr3 = 135 - 89.91 =45.09 V

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