A spherical black body of radius 12 cm radiates 450 W power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be
1800
Power radiated is given by
P=(4πr2)σT4 or P∝ r2 T4∴ P2P1=(r2r1)2×(T2T1)2=(12)2×(21)2=4Or P2=4P1=4×450=1800 W
which is choice (d)