Question

Two rods of same length and material transfer a given amount of heat in 16 seconds, when they are joined end to end. But when they are joined lengthwise (parallel), then they will transfer same heat in same conditions in

• A. 2 s
• B. 3 s
• C. 1.5 s
• D. 4 s

Answer 1

The correct option is D 4 s


$Q=KA\frac{\Delta \theta }{l}.t\therefore t\propto \frac{1}{A}$ [As Q, K and $\Delta \theta$ are constant]
$\frac{t_1}{t_2}=\frac{l_1}{l_2}\times \frac{A_2}{A_1}=\left(\frac{l_1}{\frac{l_1}{2}}\right)\times \left(\frac{2A_1}{A_1}\right)$
$\frac{t_1}{t_2}=4\Rightarrow t_2=\frac{t_1}{4}=\frac{16}{4}=4$