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posted by  xyla on 10/13/2008 9:21:36 AM  |  status: Live  

help.. DIRECT CURRENT CIRCUITS .. Thank you..

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15. Two (2) 115 - V incandescent lamps A and B are connected in series across a 230-V source. if lamp A is rated 75 watts and lamp B is rated 50 watts, determine the current drawn by the series connection.
 
a. 0.52 A
b. 0.64 A
c. 0.48 A
d. 0.57 A

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posted by Shree_vani on 10/13/2008 9:40:18 AM  |  status: Live
Asker's Rating: Lifesaver   
xyla's comment:
"Thanks"
Response Details:
 
We have
P = V2 / R
R = V2 / P
The resistance of lamp A ,
RA = (115)2 / 75 = 176.33Ω
The resistance of lamp B
RB = (115)2 / 50 = 264.5Ω
The total resistance of the  series circuit
R = RA + RB
R = 176.33 + 264.5 = 440.83Ω
Current drawn by the series circuit
I = V / R
I = 230 / 440.83
I = 0.521A
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