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posted by  showoff134 on 6/28/2008 11:11:21 PM  |  status: Closed  

Circuit multiple choice question

Course Textbook Chapter Problem
Calculus Based Physics Fundamentals of Physics Extended (8th) by Resnick, Halliday, Walker N/A N/A
Question Details:
Two identical batteries, each with an emf of 18V and an internal resistance of 1 ohm are wired in parallel by connecting their positive terminals together and connecting their negative terminals together.  The combination is then wired across a 4 ohm resistor.  The potential difference across the 4 ohm resistor is:
A. 4.0V
B. 8.0V
C. 14V
D. 16V
E. 29V

An explanation and answer would be a lifesaver for sure.
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Oracle
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posted by Kayen on 6/29/2008 1:28:53 AM  |  status: Live
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showoff134's comment:
"close but i think the other guy got the resistance right, thanks though"
Response Details:
EMF = 18 V
Total resicsatance = 4 +1 = 5 Ω
Current drawn, I = E/R' = 18/5 = 3.6 A
Potential drop
               V = I.R = 3.6x4 = 14.4 V
 
Choice C 14 V
 
 
Kayen (Enjoys helping you uderstand..)
Please do not forget to Rate my Response.
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posted by showoff134 on 6/29/2008 1:30:31 AM  |  status: Live
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Response Details:
and how do you know this?
Oracle
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posted by zsm28 on 6/29/2008 2:00:52 AM  |  status: Live
Asker's Rating: Lifesaver   
showoff134's comment:
"I think you got it right"
Response Details:
These 2 batteries are wired in parallel, so the equivalent emf = 18 V
the equivalent internal resistance is 1/2 = 0.5 Ω
the total resistance R = 4 + 0.5 = 4.5 Ω
The current I = 18/4.5 = 4 A
The potential difference across the 4 ohm resistor is 4*4 = 16 V
answer: D
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