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GATE 2026 PH – Question 17

Thermodynamics and Statistical Mechanics · Laws of thermodynamics · 1 mark · Multiple choice

Consider the Otto cycle for an ideal gas engine consisting of two quasistatic adiabatic and two quasistatic isochoric processes. The correct temperature-entropy (T-S) phase diagram for the cycle is

Four candidate temperature–entropy diagrams for an Otto cycle.
  1. Option A in the figure
  2. Option B in the figure
  3. Option C in the figure
  4. Option D in the figure

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Show answer and explanation

Correct answer: (A) Option A in the figure

Explanation

Reversible adiabats are vertical in T–S space. Isochores obey dS = Cv dT/T, so temperature increases exponentially with entropy. The engine cycle has positive enclosed heat and follows A.