Answer: 133.3 W/mK.
- A 300 W/mK
- B 150 W/mK
- C 100 W/mK
- D 133.3 W/mK
Correct answer: D. 133.3 W/mK
Explanation: For equal rods in series K = 2K<sub>1</sub>K<sub>2</sub>/(K<sub>1</sub>+K<sub>2</sub>) = 2×200×100/300 = 133.3 W/mK.
During a phase change (melting or boiling), temperature stays constant while heat is absorbed entirely as latent heat (Q=mL); temperature only rises again once the substance is fully in its new phase.
Concept context
Temperature scales, thermal expansion, calorimetry, and the three modes of heat transfer including radiation laws.