question_answer

A large cylindrical rod of length L is made by joining two identical rods of copper and steel of length \[\left( \frac{L}{2} \right)\]each. The rods are completely insulated from the surroundings. If the free end If copper rod is maintained at 100°C and that of steel at 0°C then the temperature of junction is Thermal conductivity of copper is 9 times that if steel)                                                                                                                 [JEE ONLINE 19-05-2012]

A)  90°C      

B)       50°C

C)  10°C              

D)                   67°C

Correct Answer: A

Solution :

     

[a]

Let conductivity of steel then from question

Conductivity of copper

From formula temperature of junction;