Topic: Heat Transfer
A thin copper wire at 300 °C is suddenly immersed in water at 30 °C. It cools down to 150 °C in 70 seconds. It is then reheated to the initial temperature of 300 °C and suddenly exposed to air at 30 °C where it cools down to 150 °C in 200 seconds. This difference in cooling time is due to
- A. Larger specific heat of water
- B. Larger heat transfer coefficient in water
- C. Smaller heat transfer coefficient in water
- D. None of the above
Answer: B. Larger heat transfer coefficient in water
Explanation: Water has a higher thermal conductivity than air, which means that it can transfer heat more efficiently. Hence, the difference in cooling time is due to a larger convective heat transfer coefficient in water.