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D.C circuits PLEASE help are my answers correct?

  • Thread starter natural
  • Start date
  • #1
26
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Homework Statement


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?

Homework Equations


E = IR = Ir

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
 

Answers and Replies

  • #2
26
0
***TYPO****-*********Relavant Equation should be E = IR + Ir*******
 
  • #3
berkeman
Mentor
56,819
6,787
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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