1.

Two metal rods of same length have same temperature difference between their ends. Their thermal conductivities are K_(1) and K_(2) and cross-sections A_(1) and A_(2) respectively. What is the condition for the same rates of flow of heat ?

Answer»

`(K_(1))/(K_(2))=(A_(1))/(A_(2))`
`(K_(1))/(K_(2))=(A_(2))/(A_(1))`
`K_(1)^(2)A_(2)^(2)=K_(2)^(2)A_(1)^(2)`
`K_(1)A_(1)^(2)=K_(2)A_(2)^(2)`

Solution :`(Q_(1))/(t)=(k_(1)A_(1)(T_(1)-T_(2)))/(d)`
`(Q_(2))/(t)=(k_(2)A_(2)(T_(1)-T_(2)))/(d)`
Now `(Q_(1))/(t)=(Q_(2))/(t)`
`rArr(k_(1)A_(1)(T_(1)=T_(2)))/(d)=(k_(1)A_(2)(T_(1)-T_(2)))/(d)`
`rArr""(k_(1))/(k_(2))=(A_(2))/(A_(1))`
THUS CORRECT choice is (B)


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