Question

The third law of thermodynamics states that:

• A. Energy in the universe is constant
• B. Entropy of a perfect crystal at absolute zero is zero
• C. The efficiency of any engine cannot be 100\%
• D. Temperature can be measured in a relative scale

Hint:

At absolute zero, a perfect crystal has zero entropy—this is the essence of the third law of thermodynamics. It provides a baseline for entropy calculations.

Answer 1

The Correct Option is B

Step 1: The third law of thermodynamics, also known as Nernst’s theorem, states that the entropy of a perfect crystalline substance approaches zero as the temperature approaches absolute zero (\( 0 \, \text{K} \)).
Step 2: This is because at absolute zero, the substance is in a state of perfect order, with only one possible microstate, implying zero entropy (\( S = k \ln W \), where \( W = 1 \)).
Step 3: The third law has important implications in low-temperature physics and thermodynamic calculations, as it sets a reference point for entropy.
Why the other options are incorrect:

• (A) This refers to the first law of thermodynamics (conservation of energy).
• (C) This is a result from the second law of thermodynamics, not the third.
• (D) Temperature measurement principles are unrelated to the third law.