(7%) Problem 13: Why do lights dim when a large appliance is switched on? The an

Question

(7%) Problem 13: Why do lights dim when a large appliance is switched on? The answer is that the large current the appliance motor draws causes a significant potential drop in the wires and reduces the voltage across the lights. This is called an IR drop because it is simply due to the current and resistance of the device in question Low P R2 Bulb dims R, wire Low R large , Motor ©theexpertta.com 50% Part (a) Assume the bulb in question dissipates P2 = 75 W when connected to the 120 V AC source. What average power will the bulb dissipate if11-15.5 A passes through the wires when the motor comes on? Assume a negligible change in bulb resistance, while the resistance of the wires are R1 0.35 &cohms; > 50% Part (b) How many watts are consumed on average by the motor? e wires are R1 = 0.55 &Ohms; Grade Summary Deductions Potential 0% 100% Submissions Attempts remaining: 20 (000 per attempt) detailed view sin0 78 9 cos0 cotan0asin acos0 atan0 acotan0 sinh0 cosh0 anh0cotanh0 ODegrees O Radians tan END Submit Hint lgive up Hints: 0% deduction per hint. Hints remaining: Feedback: 0% deduction per feedback.

Explanation / Answer

Part A )

we have equation

R = V2 / P

R = 1202 / 75

R = 192 Ohm

V = 120 - i1 R1

V = 111.47 volts

P = V ' 2

= 111.472 / 192

P = 64.7 W

Part B )

i1 = i2 + i3

i2 = V'/ R2

= 111.47 / 192

= 0.58 A

i3 + 0.58 = 15.5 ( given )

i3 = 14.9 A

P = V ' i3  

P = 111.47 X 14.9

P = 1660.903 W

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