ગોળીય અવકાશગંગાની દળ ઘનતા તેના કેન્દ્રથી લાંબા અંતર \('r'\) પર \(\frac{ K }{ r }\) મુજબ બદલાય છે. એક ક્ષેત્રમાં એક નાનો તારો \(R\) ત્રિજયાની વર્તુળાકાર કક્ષામાં ભ્રમણ કરે છે તો તેના માટે આવર્તકાળ \(T\) અને \(R\) વચ્ચેનો સંબંધ શું થાય?

A \(T \propto R\)
B \(T ^{2} \propto \frac{1}{ R ^{3}}\)
C \(T ^{2} \propto R\)
D \(T ^{2} \propto R ^{3}\)

Verified Solution

Answer & Solution

Correct Answer

(C) \(T ^{2} \propto R\)

Step-by-step Solution

Detailed explanation

\(dm =\rho dv\) \(dm =\left(\frac{ k }{ r }\right)\left(4 \pi r ^{2} dr \right)\) \(dm =4 \pi krdr\) \(M =\int_{0}^{ R } d m =\int_{0}^{ R } 4 \pi krdr\) \(M=\left.4 \pi k \frac{r^{2}}{2}\right|_{0} ^{R}\) \(M =2 \pi k \left( R ^{2}-0\right)\) \(M =2 \pi kR ^{2}\) for circular…

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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