# Temperature difference of 120°C is maintained between two ends of a uniform rod AB of length 2L.

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Temperature difference of 120°C is maintained between two ends of a uniform rod AB of length 2L. Another bent rod PQ, of same cross-section as AB and length $3L\over2$, is connected across AB (See figure). In steady state, temperature difference between P and Q will be close to :

(1) 60ºC

(2) 75ºC

(3) 35ºC

(4) 45ºC

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Ans: (4) 45ºC

Sol:

${\Delta T\over R_{eq.}}=I={(120)5\over8R}$

$\Delta T_{PQ}={120\times5\over8R}\times{3\over5}R={360\over8}=45°C$