Question

Three substances A, B and C of same mass are present at their respective melting points. On heating, if they melt completely in 5 minutes, 7 minutes and 3 minutes respectively, then which substance has the highest specific latent heat? (Assume heat is absorbed at the same rate)

• A. Substance A
• B. Substance B
• C. Substance C
• D. All the substances have same specific latent heat

Hint:

For a phase change at a constant rate of heating, the time taken is directly proportional to the specific latent heat of the substance.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Latent heat of fusion (\( L \)) is the heat required to change a substance from solid to liquid without changing its temperature.
Step 2: Key Formula or Approach:
\[ Q = m \cdot L \]
Since heat is absorbed at a constant rate (\( P \)), total heat \( Q = P \cdot t \).
Step 3: Detailed Explanation:
Combining the formulas: \( m \cdot L = P \cdot t \).
Since mass (\( m \)) and power (\( P \)) are the same for all three:
\[ L \propto t \]
The substance that takes more time to melt completely requires more total heat, implying it has a higher specific latent heat.
Substance B takes the longest time (7 minutes).
Step 4: Final Answer:
Substance B has the highest specific latent heat.