A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be :

1. 450

2. 1000

3. 1800

4. 225

Doubtly Asked 30 Oct 2026 NEET UG 2017 neet Save WhatsApp Report

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Best answer

Answer: 3. 1800

Key idea: power radiated \(P=\sigma AT^4\propto r^2T^4\).

Radius halved gives factor \(\tfrac14\); temperature doubled gives factor \(2^4=16\).

\(P'=450\times\tfrac14\times16=1800\) W.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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