Question

A beaker is filled with water at 4° C. One time temperature is increased by few degrees above 4° C and another time it is decreased few degrees below 4° C. One shall observe that

• A. The level remains constant in each case
• B. In the first case water overflows while in second case it comes down
• C. In first case water comes down while in second case it over flows
• D. Water overflows in both cases

Hint:

Remember the graph of density of water vs. temperature. It's a curve with a peak at 4°C. Moving away from 4°C in either direction (heating or cooling) results in a decrease in density and an increase in volume. This unique property is crucial for aquatic life in cold climates, as it causes lakes to freeze from the top down.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
This question is based on the anomalous expansion of water. Unlike most substances which continuously expand when heated and contract when cooled, water has a unique behavior around 4°C. Water has its maximum density (and thus, minimum volume for a given mass) at approximately 4°C.

Step 2: Detailed Explanation:
Let's analyze the two scenarios, starting from a beaker completely filled with water at 4°C.

• Initial State: The water is at 4°C, its point of maximum density and minimum volume. The beaker is full to the brim.

• Case 1: Temperature is increased above 4°C.
When water is heated from 4°C to a higher temperature (e.g., 10°C), its density decreases. Since density = mass/volume, a decrease in density for a constant mass means the volume must increase. As the volume of the water increases, and the beaker is already full, the excess volume of water will spill out or overflow.

• Case 2: Temperature is decreased below 4°C.
When water is cooled from 4°C to a lower temperature (e.g., 1°C), its density also decreases due to its anomalous behavior. Again, a decrease in density means the volume must increase for the same mass of water. As the volume of the water increases, it will again overflow from the full beaker.
Conclusion:
In both cases—heating above 4°C and cooling below 4°C—the water expands (its volume increases). Since the beaker was initially full, this expansion will cause the water to overflow in both scenarios.

Step 3: Final Answer:
The water overflows in both cases.