Question:

A spherical black body with a radius of 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:

450

1800

225

900

Q=σAT⁴
If r₂ = r₁/2 and A₂ = A₁/4 (∝A∝r²), T₂ = 2T₁
Q₂/Q₁ = (A₁/4)(16T₁⁴)/A₁T₁⁴ = 4
Q₂ = 4Q₁ = 4 × 450 = 1800