1. Heat is conducted through the two slabs shown in the drawing. The slabs have

Question

1. Heat is conducted through the two slabs shown in the drawing. The slabs have identical thicknesses and cross sectional areas, but they are made from different materials. The thermal conductivity of slab 1 is k1 = 82 J/(s·m·C°). What is the thermal conductivity k2 of slab 2?

2. The wings of a soaring eagle are fully spread, but not moving. As the eagle glides through the air, it’s also gaining altitude. Which one of the three methods of heat transfer is responsible for this gain in altitude?

a. Covection

b. Radiation

c. Conduction

Explanation / Answer

The rate of heat lost by the slab1 = The rate of heat gain by the slab2

thus, K1 A1 dT1 /t1 = K2 A2 dT2 /t2

since these slabs are identical thickness and areas A1=A2 and t1= t2

now , the above equation turned as,

K1 dT1 = K2 dT2

given: K1 = 82 J /s.m.oC,

dT1 = 65-45 = 20 oC,

dT2 = 45-35 = 10 oC,

K2 = ?

82(20) = K2 ( 10 )

K2 = 164 J /smoC,

thus,

thermal conductivity of slab 2 = 164 J /s.m.oC.

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