Question

Two copper spheres of radii 6 cm and 12 cm respectively are suspended in an evacuated enclosure. Each of them are at a temperature 15°C above the surroundings. The ratio of their rate of loss of heat is.................

1. 2:1
2. 1:4
3. 1:8
4. 8:1

Answer 1

(b) 1:4

r₁ = 6 cm
r₂ = 12 cm
T₁ = T₂ = 15°C
Ratio of loss of heat is

`R_1/R_2=A_1/A_2xxT_1^4/T_2^4`

`R_1/R_2=(4pir_1^2)/(4pir_2^2)=6^2/12^2=1/4`