Question

Two identical beakers with negligible thermal expansion are filled with water to the same level at ${}^o$C. If one say A is heated while the other B is cooled, then :

• A. water level in A must rise
• B. water level in B must rise
• C. water level in A must fall
• D. water level in B must fall

Answer 1

Answer: (A), (B)

The correct options are
A water level in A must rise
B water level in B must rise

$Answer:-$ A,B

Thermal expansion is the tendency of matter to change in shape, area, and volume in response to a change in temperature, through heat transfer. Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, the kinetic energy of its molecules increases.. The unusual behaviour of water between 0°C and 4°C i.e., contraction of water when heated from 0°C to 4°C is known as the anomalous expansion of water.

The density is the mass per unit volume of a substance and that mass of a given quantity of a substance does not change. So when volume changes density changes. Since water contracts form 0°C to 4°C,its volume decreases and the density increases to reach the maximum value at 4°C. When water is cooled from 100°C it contracts till it reaches 4°C; then it expands.

Since water contracts on melting and on heating from 0°C to 4°C

So in both beaker water must rise.