Problem 21.38 In a string of holiday lights, 70 lights-with a resistance of 14.5

Question

Problem 21.38 In a string of holiday lights, 70 lights-with a resistance of 14.5 each-are connected in series Part A If the string of lights is plugged into a 120-V outlet, what current flows through it? Express your answer to three significant figures and include appropriate units. Value Units Submit My Answers Give Up Part B Five of the lights burn out and activate their shunt resistors, effectively reducing the resistance of each one to 0.17 . How much current now flows through the entire string of lights? Express your answer to three significant figures and include appropriate units. alue Units Submit My Answers Give Up Provide Feedback Continue

Explanation / Answer

Resistance of one bulb = 14.5 ohm

So net resistance of all bulbs (R)= 70×14.5 = 1015 ohm

Part (A) Voltage (V) = 120 V

So current (i) = V/R = 120/1015 = 0.118 A

Part (B) resistance of 5 fused bulbs became 0.17 ohm so net resistance of those 5 fused bulbs = 5×0.17 = 0.85 ohm

Net of remaining 65 bulbs = 65×14.5 ohm = 942.5 ohm

So net resistance of all bulbs = 942.5+0.85 = 943.35 ohm

So current flown = (i) = 120/943.35 = 0.127 A

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