Physics [2 Mark Question Answer]

The melting point of ice decreases by the increase in pressure. The melting point of ice decrease by 0.0072oC for every one atmosphere rise in pressure.

The melting point of ice decreases by the presence of impurity in it.
Use: In making the freezing mixture by adding salt to ice. This freezing mixture is used in preparation of ice creams.

(i) Average kinetic energy of molecules changes.
(ii) Average potential energy of molecules changes.

Heat supplied to a substance during its change of state, does not cause any rise in its temperature because this is latent heat of phase change which is required to change the phase only.

The reason is that the heat energy required for melting the frozen lake is absorbed from the surrounding atmosphere. As a result, the temperature of the surrounding falls and it became very cold.

The reason is that after the hail storm, the ice absorbs the heat energy required for melting from the surrounding, so the temperature of the surrounding falls further down and we feel colder.

(a) 1 g ice at 0oC requires more heat because ice would require additional heat energy equal to latent heat of melting.

(b) 1 g ice at 0oC first absorbs 336 J heat to convert into 1 g water at 0oC.

Latent heat: The heat energy exchanged in change of phase is not externally manifested by any rise or fall in temperature, it is considered to be hidden in the substance and is called the latent heat.

The specific heat capacity of a substance is the amount of heat energy required to raise the temperature of unit mass of that substance through by 1oC (or 1K).
S.I. unit is joule per kilogram per kelvin (Jkg-1K-1).

The heat capacity of a body is the amount of heat energy required to raise its temperature by 1oC or 1K.
S.I. unit is joule per kelvin (JK-1).

The quantity which determines the direction of flow of heat between two bodies kept in contact is called temperature.
S.I. unit kelvin (K).

One calorie of heat is the heat energy required to raise the temperature of 1 g of water from 14.5oC to 15.5 oC.
1 calorie = 4.186 J

By making the base of a cooking pan thick, its thermal capacity becomes large and it imparts sufficient heat energy at a low temperature to the food for proper cooking. Further, it keeps the food warm for a long time after cooking.

The specific heat capacity of liquid X is higher than that of Y. So, for same mass and same heat energy, the rise in temperature for X will be less than that of Y.

As a coolant in car radiators, the liquid needs to absorb more energy without much change in temperature. So, liquid X is ideal for this function.

The reason is that water does not cool quickly due to its large specific heat capacity, so a hot
water bottle provides heat energy for fomentation for a long time.

The principle of method of mixture:
Heat energy lost by the hot body = Heat energy gained by the cold body.
This principle is based on law of conservation of energy.

Heat capacity of liquid A is less than that of B.
As the substance with low heat capacity shows greater rise in temperature.

The expression for the heat energy Q
Q= mc Δ t (in joule)