दो एकसमान सेल प्रत्येक का विद्युत् वाहक बल \((emf)\) \(1.5\,V\) है, दो समान्तर क्रम में संयोजित प्रतिरोधों प्रत्येक का प्रतिरोध \(20\,\Omega\) है, के सिरों पर समान्तर क्रम में जोड़े जाते है। एक वोल्टमीटर परिपथ में जुड़ा है जिसका मापन \(1.2\,V\) है। प्रत्येक सेल का आन्तरिक प्रतिरोध है \(........... \, \Omega\)

A \(2.5\)
B \(4\)
C \(5\)
D \(10\)

Verified Solution

Answer & Solution

Correct Answer

(C) \(5\)

Step-by-step Solution

Detailed explanation

\(V = E - ir / 2\) \(1.2=1.5- i \left(\frac{ r }{2}\right)\) \(i \frac{ r }{2}=0.3\) \(i =\frac{1.5}{10+\frac{ r }{2}} \Rightarrow 10 i +\frac{ ir }{2}=1.5\) \(10 i =1.5-0.3\) \(i =0.12\, A\) \(\Rightarrow r =\frac{0.6}{0.12}=5 \,\Omega\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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