Questions
Two metallic spheres P and Q are of same surface finish and same density. Weight of P is twice that of Q. Both spheres are heated to same temperature and are left in room to cool by radiation. The ratio of initial rate of cooling of P to that of Q is
detailed solution
Correct option is C
Let the mass of Q be m.∴mass of P = 2mNow, −m.s.dTdt=eσ.(4πR2)(T4−T04)⇒−dTdt=eσ.(4πR2)43πR3ρS(T4−T04)⇒−dTdt=3eσρS1R(T4−T04)∴−dTdt∝1RNow 43πRp3ρ=2×43πRQ3ρ⇒Rp=(2)1/3.RQ∴Initial rate of cooling of PInitial rate of cooling of Q=RQRP=1(2)1/3Similar Questions
For a black body at temperature 727°C, its radiating power is 60W and temperature of surrounding is 227° C. If temperature of black body is changed to 1227°C, then its
radiating power will be :
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