Physics [2 Mark Question Answer]

Principle of Calorimetry:
When a hot body is mixed or kept in contact with a cold body, there is a transfer of heat from hot body to cold body such that
Total heat gained by colder body = Total heat lost by the hot body,
if there is no loss of heat to the surroundings.

Water has a high specific heat capacity. So, water extracts much heat without much rise in temperature. By allowing water to flow in radiator pipes of the vehicles, heat energy form such parts is removed. Hence, it is used as a cooling agent in the radiators of automobiles.

Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. The sun's heat warms the surface water a lot more than the deep ocean water, and this temperature difference creates heat energy. Thus, oceans are known as storehouse of heat energy. Just a small portion of the heat trapped in the ocean could power the world.

1 kg of ice at 0°C absorbs 336000 J of heat energy to convert into water at 0°C. Therefore,1 kg of water at 0°C has 336000 J heat energy more than 1 kg ice at 0°C. So, ice appears colder than water.

Latent heat is the quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to water or water to steam, at constant temperature. 

Latent heat of vapourisation of water, L=540 cal/g
Mass of water, m=100g
Amount of heat required convert 100g of water at 100°C into steam at 100°C = m x L = 100 x 540 = 5.4 kJ

Atmosphere is usually warm during snowfall because each kilogram of ice on melting absorbs 336000 J of heat from atmosphere. 

Whenever a substance goes through a phase change (like boiling), the energy goes into breaking up the interactions between molecules, and so the temperature stays constant until all the interactions are broken. Once whole of the substance has boiled, then any added heat will act to raise them temperature again.

A change of state is a change in the object from a solid to liquid or from a solid to gas or from liquid to solid. Ice changing into water is an example of a change in state. 

Ice melts under pressure. So, when the steel blades of the skates pressed on the ice, the ice melts. The water formed makes the skates slide easily over the ice, reducing friction. So, when we are skating on ice, we are skating on a thin film of water, which acts like lubricating oil. Nothing such happens in case of glass.

Temperature is a physical property that quantitatively expresses the common notions of hot and cold. It is the degree of hotness or coldness of a body or environment.

Celsius scale and Fahrenheit scale are two commonly used scales of temperature because the former is based on the freezing point of water as 0°C and boiling point of water as 100°C. The same points on the Fahrenheit scale are 32°F and 212°F.

Two scales for measuring temperature are
i. Celsius scale
ii. Fahrenheit scale

SI unit of:
i. Amount of heat - joule
ii. Heat Capacity - joule per Kelvin
iii. Specific Heat Capacity - joule per kilogram per Kelvin

Principle of Calorimetry:
When a hot body is mixed or kept in contact with a cold body, there is a transfer of heat from hot body to cold body such that
Total heat gained by colder body = Total heat lost by the hot body,
if there is no loss of heat to the surroundings.

Heat capacity of a body is the quantity of heat required to raise its temperature by 1°C. It depends upon the mass and the nature of the body.
Units: J/°C or calorie/°C

(i) In cooling - Water is used in the cooling systems of automobiles and other engines.
(ii) As heat reservoir - In cold countries, water is used as a reservoir for wine and juice to avoid their freezing. The reason is that water can provide more heat to the bottles due to its high specific heat capacity. Hence, they do not cool down further to freeze.

Although both ice cubes and iced water are at 0°C but ice cubes cool more quickly because each gram of ice requires additional 80 calories of heat to get converted into water at the same temperature, i.e., at 0°C. Hence, the cooling capacity of ice cubes is more than that of iced water.

Ice cream appears colder to mouth than water at 0°C because it can extract approximately 80 cal/g (latent heat of fusion of ice)more heat from as compared to water at 0°C.

Steam at 100°C will produce more severe burns because every gram of steam gives out 2260 J of heat energy while condensing. This much amount of heat is additional to the heat contained in one gram of boiling water.

Lumps of ice cool better than cold water because each gram of ice requires additional 80 calories of heat to get converted into water. Hence, cooling capacity of lumps of ice is more than cold water.

Steam burn is worse than a hot water burn because 1 g of steam gives out 540 calories of additional heat.

Sand improves the friction between car tyres and the road, so cars don't skid on icy surfaces. Salt is spread so as to decrease the melting point of ice. Ice on the roads melt, making the roads less slippery.

Ice melts under pressure. So, when the steel blades of the skates pressed on the ice, the ice melts. The water formed makes the skates slide easily over the ice, reducing friction. So, when we are skating on ice, we are skating on a thin film of water, which acts like lubricating oil. Nothing such happens in case of glass.