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Discussion :: Heat and Mass Transfer

  1. Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of

    2. A.

     1:1
    B.

     2: 1
    C.

     1: 2
    D.

     4: 1

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    Workspace

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    Answer : Option C

    Explanation :

    Correct Option is (D)

    Rate of heat transfer by radiation = A x T4 Temperature is same for both spheres A = Surface area Surface area of sphere = π d2 Cooling rate of big sphere / Cooling rate of small sphere = d2 big / d2small Hence cooling rate will takes place in the ratio of 4 : 1

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