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Two metal blocks M1 and M2 of equal cross-sectional area are joined end to end in series. The free face of M1 is at 100°C, the junction is at 80°C, and the free face of M2 is at 0°C. M1 is 16 cm long and M2 is 8 cm long, with M2 having thermal conductivity K. In steady state, find the thermal conductivity of M1.

1. 10 K
2. 8 K
3. 12.5 K
4. 2 K

Correct answer: 8 K

Solution

Equating the steady-state heat current in both blocks and inserting the lengths and temperature drops gives K1 = 8K.

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