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The Sun rotates around its centre once in 27 days. What will be the period of revolution if the Sun were to expand to twice its present radius without any external influence? Assume the Sun to be a sphere of uniform density.

Asked in NEET 2025 · Conservation of angular momentum

• (1) 115 days
• (2) 108 days
• (3) 100 days
• (4) 105 days

Step-by-step solution

Why the other options are wrong

• (1) comes from no single slip reproduces 115 days; as a check, T∝ R² at fixed mass forces the period to grow by exactly 4, and 115/27=4.26
• (3) comes from no single slip reproduces 100 days; it corresponds to a growth factor 100/27=3.70, whereas doubling the radius multiplies I by exactly 4
• (4) comes from no single slip reproduces 105 days; it corresponds to a growth factor 105/27=3.89, again short of the exact 4 that I∝ R² demands

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