Two cylinders P and Q have the same length and diameter and are made of different materials having thermal conductivities in the ratio 2 : 3. These two cylinders are combined to make a cylinder. One end of P is kept at 100°C and another end of Q at 0°C. The temperature at the interface of P and Q is [MP PMT 1994; EAMCET 2000]

• A.            \[{{30}^{o}}C\]         
• B.            \[{{40}^{o}}C\]
• C.            \[{{50}^{o}}C\]         
• D.            \[{{60}^{o}}C\]