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 :



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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