JEE Main 2026 — Thermodynamics (C) Question with Solution
JEE Main 2026 (23 January Shift 1)
Question
A cup of water at (system) is placed in a microwave oven and the oven is turned on for one minute during which the water begins to boil. Which of the following option is true ?
Choose an option
Show full solutionCorrect option: D
Correct answer
D
Step-by-step explanation
For water heating in a microwave:
Heat (q): The microwave radiates electromagnetic energy that is absorbed by water molecules, so q = +ve
Work (w): As water heats and boils, it expands against atmospheric pressure. The system does work on the surroundings, so w = -ve
Internal Energy (ΔU): From the first law, ΔU = q + w. Since heat absorbed (+ve) is much larger in magnitude than work done against atmosphere (-ve), the net change is ΔU = +ve (confirmed by temperature increase from 5°C to boiling)
Therefore: q = +ve, w = -ve, ΔU = +ve
Heat (q): The microwave radiates electromagnetic energy that is absorbed by water molecules, so q = +ve
Work (w): As water heats and boils, it expands against atmospheric pressure. The system does work on the surroundings, so w = -ve
Internal Energy (ΔU): From the first law, ΔU = q + w. Since heat absorbed (+ve) is much larger in magnitude than work done against atmosphere (-ve), the net change is ΔU = +ve (confirmed by temperature increase from 5°C to boiling)
Therefore: q = +ve, w = -ve, ΔU = +ve
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This is a previous-year question from JEE Main 2026, covering the Thermodynamics (C) chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.