JEE Main 202623 JanuaryMorning Shift
- Exam
- JEE Main
- Year
- 2026
- Date
- 23 January
- Shift
- Morning Shift
- Subject
- Chemistry
- Chapter
- Thermodynamics (C)
JEE Main 2026 · 23 January · Morning Shift · Chemistry · Thermodynamics (C)
A cup of water at 5^ C (system) is placed in a microwave oven and...
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 ?
Options
- A
- B
- C
- D
Correct answer
D.
Step-by-step solution
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