There are two identical vessels filled with equal amounts of ice. The vessels are of different metals., If the ice melts in the two vessels in $20$ and $35$ minutes respectively, the ratio of the coefficients of thermal conductivity of the two metals is
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(b) $Q = \frac{{KA({\theta _1} - {\theta _2})}}{l}t = $ $ \Rightarrow {K_1}{t_1} = {K_2}{t_2}$ $ \Rightarrow \frac{{{K_1}}}{{{K_2}}} = \frac{{{t_2}}}{{{t_1}}} = \frac{{35}}{{20}} = \frac{7}{4}$
(As $Q$ , $l$ , $A$ and $({\theta _1} - {\theta _2})$ are same)
(As $Q$ , $l$ , $A$ and $({\theta _1} - {\theta _2})$ are same)
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