A solid sphere and a hollow sphere of the same material and of equal radii are heated to the same temperature.

Answer

A, B, D

Explanation

E=Energy radiated per unit area per unit time
Rate of heat flow =Energy radiated
(a) Energy per unit time` =ExxA`
`So, E_(Al)=(eOT^4xxA)/(eOT^4xxA')`
`=(4 pi r^2)/(4pi (2r)^2)=1:4`
`(b) Emissivity of both are same`
` (M_1s_2dT_1)/(M_1s_2dT_2)=1`
`implies (dT_1)/(dT_2)=(M_2s_2)/(M_1s_1)`
=(rho_(2)4 pi r_(2)^(3)xxs_2)/(rho_(1)4 pi r_(1)^(3)xxs_(1))`
`(1xx3.4xx8 pi xx390)/(4xx1xxpixx90)`
`2.9:1`.