Two rods made of same material, have same thermal conductivities and area of cross-section. It is observed that to conduct same amount of heat between temperatures T1 and T2, rod 1 takes twice the time as the other. Find the ratio of their lengths.
A
2:1
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B
1:3
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C
1:1
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D
√2:1
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Solution
The correct option is A2:1 Given, k1=k2,A1=A2,Q1=Q2 and t1=2t2
We know that, Q=kA(T1−T2)tl ∴Q1Q2=k1k2×A1A2×t1t2×l2l1 ⇒t1t2=l1l2 ⇒l1l2=21 ∴ option (a) is correct.