Question

A steel and a copper bar are joined end to end. The area of the steel bar is half the area of the copper bar. Their lengths are equal to 10cm each. Temperature of free ends of steel & copper rod are 0°C & 100°C respectively. KS = 50 J/smK & KC =384 J/smK. Calculate equivalent thermal conductivity of the combined bar.

(a) 63°C

(b) 63K

(c) 336°C

(d) 36K

Answer 1

Correct choice is (a) 63°C

To elaborate: Temperature at the fixed ends of both rods will be the same.

KS AS (T-0)/LS = KC AC (100-T)/ LC

∴ 50*1/2 LCT = 384* C (100-T)

⇒ 25T = 38400 – 384T

⇒ T = 63°C.