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  4. Two identical rods of a metal are welded as shown in figure-4.39(a). 20 cal of heat flows through them in 4 minute. If the rods are welded as shown in figure-4.39(b), then the same amount of heat will flow in :

Q. Two identical rods of a metal are welded as shown in figure-4.39(a). $20\, cal$ of heat flows through them in $4$ minute. If the rods are welded as shown in figure-4.39(b), then the same amount of heat will flow in :Physics Question Image

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Solution:

As we use $20=\frac{k A(100-0) t_{1}}{2 L}$ ...(1)
$\Rightarrow 20=Q=\frac{k(2 A)(100-0) t_{2}}{L}$ ...(2)
$\Rightarrow \frac{t_{1}}{2}=2 t_{2}$
$\Rightarrow t_{2}=\frac{t_{1}}{4}=\frac{4}{4}=1\, \min$

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