Q. 24

An aluminium rod and a copper rod of equal length 1.0 m and cross-sectional area 1 cm2 are welded together as shown in figure. One end is kept at a temperature of 20°C and the other at 60°C. Calculate the amount of heat taken out per second from the hot end. Thermal conductivity of aluminium = 200 Wm–1 °C–1 and of copper = 390 Wm–1 °C–1.



Answer :


Given


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Area of cross section


A =1 cm2


=1×10–4 m2


Thermal conductivity of aluminium, KAl = 200 W/m°C



copper, KCu = 390 W/m°C


Now since these rods are connected in parallel,


So heat flowing per second


= qAl + qCu


= KAl × ∆T + KCu ×A× ∆T


= KAl A × (60-20) + KCu A × (60-20)


= 1×10–4 m2 × 40 (200+ 390)


= 2.36 W


Heat drawn in 1 second = 2.36 W


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