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ICSEClass XMathematicsMensuration01 Mark2026 Moderate

QQuestion

The total surface area of a sphere S₁ of radius R and the total surface area of a solid hemisphere S₂ of radius r are equal. The ratio R : r is:

The total surface area of a sphere S₁ of radius R and the total surface area of a solid hemisphere S₂ of radius r are equal

(a) 1 : 1

(b) 2 : 1

(c) √3 : 2

(d) 2 : √3

Exam-ready answer • 01 Mark

Answer

(c) √3 : 2

Explanation:

Total surface area of sphere S₁ = 4πR²

Total surface area of solid hemisphere S₂ = 3πr²

Since the total surface areas are equal:

4πR² = 3πr²

⇒ 4R² = 3r²

⇒ \frac{R^2}{r^2}=\frac{3}{4}

⇒ \frac{\mathrm{R}}{\mathrm{r}}=\frac{\sqrt{3}}{2}

Therefore, R : r = √3 : 2.

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