Question

5. Two metal rods, one silver and the other gold, are attached to each other. The free end of the silver rod is connected to a steam chamber, with a temperature of 100°C, and the free end of gold rod to an ice water bath, with a temperature of 0°C. The rods are 5.0 cm long and have a square cross-section, 2.0 cm on a side. How much heat flows through the two rods in 60 s? The thermal conductivity of silver is 417 W/(m«K), and that of gold is 291 W/m K). No heat is exchanged between the rods and the surroundings, except at the ends. A) 8.2 KJ B) 9.5 KJ C) 12 KJ D) 14 KJ E) 16 KJ Answer: A

Answer 1

Solution-

Thermal Resistance R can be found using

R= L/Ak1 + L/Ak2 = L/A(1/k1 + 1/k2)

Putting the values in the equation

= (5/2^2) (1/417+1/291)*10^2 = 0.7293 K/W

Q = ΔT/R

Q = (100-0)/0.7293 = 137.11 W

Now in 60 s, heat transferred = 137.11*60

= 8226.9 J

= 8.2 kJ