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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Electric Current in Conductors

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Electric Current in Conductors

Two nonideal batteries are wired in parallel. Evaluate the...

Two nonideal batteries are wired in parallel. Evaluate the following statements:
(A) The equivalent emf is smaller than either of the individual emfs.
(B) The equivalent internal resistance is smaller than either of the individual internal resistances.

Options

  1. AA is correct but B is incorrect
  2. BB is correct but A is incorrect
  3. CBoth A and B are correct
  4. DBoth A and B are incorrect

Correct answer

B. B is correct but A is incorrect

Step-by-step solution

For two batteries connected in parallel with emfs E1E_1 and E2E_2 and internal resistances r1r_1 and r2r_2, the equivalent emf is given by Eeq=E1r2+E2r1r1+r2E_{eq} = \dfrac{E_1 r_2 + E_2 r_1}{r_1 + r_2}.

This expression shows that EeqE_{eq} is a weighted average of E1E_1 and E2E_2. Thus, EeqE_{eq} always lies between E1E_1 and E2E_2 and cannot be smaller than both individual emfs. Hence, statement A is incorrect.

The equivalent internal resistance is given by the parallel combination of the individual internal resistances, req=r1r2r1+r2r_{eq} = \dfrac{r_1 r_2}{r_1 + r_2}.

In a parallel combination of resistors, the equivalent resistance is always strictly less than the smallest individual resistance. Hence, statement B is correct.
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