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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.................
- 2:1
- 1:4
- 1:8
- 8:1
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Solution
(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`
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