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D.C circuits PLEASE help...are my answers correct?

by natural
Tags: answers, circuits, correct, helpare
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natural
#1
Feb27-07, 03:47 PM
P: 27
1. The problem statement, all variables and given/known data
To find the emf and internal resistance of an unmarked battery you are given two resistor of value 5.0(ohms) and an ammeter. When the resistors are connected in parallel the current drawn from the battery is 2.0A. What are the e.m.f and internal resistance of the battery?

Am i going right?
2. Relevant equations
E = IR = Ir

3. The attempt at a solution
Series
R = 5(ohms) + 5(ohms) = 10(ohms)

Parellel
1/R = 1/5 + 1/5 = 2/5
R = 2.5(ohms)

E = 0.75*10 + o.75*r
E = 7.5 + 0.75r ------- (1)

E = 2*2.5 + 2r
E = 5 + 2r ---------- (2)

7.5 + 0.75r = 5 +2r
2.5 = 1.25r
2(ohms) = r

there for r in equation 1 gives
E = 7.5 + 0.75(2)
= 9V
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natural
#2
Feb27-07, 03:49 PM
P: 27
***TYPO****-*********Relavant Equation should be E = IR + Ir*******
berkeman
#3
Feb27-07, 03:59 PM
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berkeman's Avatar
P: 41,320
You didn't include the series combination part in your problem statement. But looking at your work, it would appear that you get 750mA when you connect them in series?

If so, then the rest looks correct.


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