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In the circuit diagram above, the ammeter reads a current of 3A when R is...

Physics
JAMB 1988

In the circuit diagram above, the ammeter reads a current of 3A when R is 5 ohms and 6A when R is 2ohms, the value of the unknown resistance X is

  • A. 1
  • B. 2
  • C. 3
  • D. 4
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Correct Answer: Option A
Explanation

E = I( R + r ) but r = 0 and effective resistance = R + X 

E = I(R + X )

E = 3( 5 + X ) .......................I

E = 6(2 + X) ........................II

since E = E

3(5 + X) = 6( 2 + X) 

15 + 3X = 12 + 6X 

15 - 12 = 6X - 3X

3X = 3

X = 1


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