Two spherical black bodies of radii R1 and R2 having surface temperatures T1 and T2 respectively radiate the same powers; then R1/R2 is equal to:
T1T24
T2T14
T2T12
T1T22
E1=E2 σ 4 πR21t T14=σ4πR22tT42 R1R2=T2T212