Physics [2 Mark Question Answer]

The rising temperature will lower water quality in lakes and oceans through a fall in oxygen concentrations, release of phosphorus from sediments and increased thermal stability due to which many marine species will either die or they will become extinct.

(i) It is responsible for the climate changes in different parts of the world and it has forced people to migrate from one place to the other.
(ii) It has affected blooming season of the different plants.

The quantity of heat given to body depends on:
(i) The mass of the body, (ii) The rise (or fall) in the temperature of the body, and (iii) Nature of the material of the body.

The reason is that sweat from our body evaporates faster under a moving fan due to rapid movement of air and so a cooling sensation is caused which makes us more comfortable.

Specific latent heat of vapourization is the quantity of heat required to convert unit mass of a substance from liquid to vapour state without change of temperature.

Specific latent heat of fusion: The specific latent heat of fusion of a substance is the heat energy released when a unit mass of substance converts from liquid to solid state without the change in temperature.

Athletes perspire profusely after competing in an event. The latent heat of evaporation of the ‘sweat’ is withdrawn from the body itself and therefore, cools the body. Hence, if they do not put on extra clothes, they are likely to catch cold.

Each 1 g of ice absorbs nearly 336 J of heat when melts to water at 0°C. Hence, it is more effective in cooling than the ice-water.

(i) Inter molecular space changes.
(ii) Intermolecular space increases.

During the state change heat supplied increases potential energy of molecules as distance between molecules increases work is done by heat supplied against attractive force.

Expression for the heat energy liberated by hot body

= mcΔQ i.e., H = mcΔQ
where m is mass, c is specific heat capacity, ΔQ is the change in temperature.

Copper is preferred over other metals for making calorimeters because:
(i) It has a low specific heat capacity.
(ii) It takes negligible amount of heat from its contents to attain the temperature of the contents.

(i) Calorie: It is the quantity of heat required to raise the temperature of 1 gm of water by 1°C (more accurately the rise in temperature is taken from 14.5°C to 15.5°C).
(ii) Kilo calorie: It is the quantity of heat required to raise the temperature of 1 kg of water by 1°C. It is equivalent to 1000 calories.

Hot water bottles are used for fomentation since since water does not cool quickly due to its large specific heat capacity.
Water is used as an effective coolant because of its large specific heat capacity due to which it can extract more heat.

(i) Water is used as an effective coolant in radiator of a car.
(ii) Hot water bottles are used for fomentation.

Heat is a form of energy, which when absorbed by a body makes it hot and when extracted from a makes it cold. It is also defined as the total kinetic energy possessed by all the molecules of a body. The S. I. unit of heat is joule/kg kelvin.