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

I had been asked this question in an online interview.

This interesting question is from Thermal Properties of Matter topic in chapter Thermal Properties of Matter of Physics – Class 11

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.