UPSC Prelims 2001 Q105: Science & Technology – Physics
When water is heated from 0 °C to 10 °C, its volume
- (a) increases
- (b) decreases
- (c) does not change
- (d) first decreases and then increases
Answer: (d) first decreases and then increases
Explanation
Change in volume of water heated from 0 °C to 10 °C
| Temperature range | Volume |
|---|---|
| 0 °C to 4 °C | Decreases — anomalous expansion; water is densest at 4 °C |
| At 4 °C | Minimum volume, maximum density (about 1 g/cm³) |
| 4 °C to 10 °C | Increases — normal expansion |
| Overall | First decreases, then increases |
Water behaves unusually between 0 °C and 4 °C: it contracts on heating. Above 4 °C it expands like other liquids. So from 0 °C to 10 °C its volume first decreases and then increases.
Answer: (d) first decreases and then increases.
Why each option is right or wrong
- (a) Incorrect. Volume first falls between 0 °C and 4 °C.
- (b) Incorrect. Above 4 °C the volume rises again.
- (c) Incorrect. The volume does change.
- (d) CORRECT. Volume falls up to 4 °C, then rises.
Key point
Anomalous expansion keeps lakes from freezing solid: 4 °C water sinks, and ice floats on top, insulating the water below.
Remember
0 → 4 °C contracts; above 4 °C expands.
Common mistakes
- Assuming all liquids simply expand on heating.
- Forgetting the special point at 4 °C.
- Thinking ice is denser than liquid water.
Exam tip
Water is densest at 4 °C — remember the number.
Sources
- NCERT Class XI — Physics Part II, chapter 'Thermal Properties of Matter' (anomalous expansion of water)
- NCERT Class IX — Science, chapter 'Matter in Our Surroundings'