### HEAT

Archimedes the father of modern mathematics lived during 287 - 212 B.C. There is no school boy who does not know the story of Archimedes ''discovery of the principle of displacement''.
Archimedes' military inventions were spectacular. He devised cranes and multipullies which would enable a single man to lift the enemy's vessels out of water.
He was so absorbed in Geometry that he died unaware of a Roman soldier who ran his sword through him.
Key Words
* Temperature and Heat
* Thermal equilibrium
* Specific heat
* Internal energy of the system
* Calorie
* Condensation
* Dew and Fog
* Melting
* Latent heat of vopourization
* Kinetic energy
* Temperature and Kinetic energy
* Method of mixtures principle
* Absolute temperature
* Evaporation
* Humidity
* Boiling
* Freezing
* Joule
* Celsius scale
* Kelvin scale

Key words - Explanation:
Temperature: Temperature is a measure of thermal equilibrium.
Conventional Definition: Temperature is 'the degree of hotness or coldness'.
Heat: Heat is a form of energy in transit, that flows from a body at a higher temperature to a body at a lower temperature.
Thermal equilibrium: When two bodies are placed in thermal contact, heat energy will be transferred from the 'hotter' body to the 'colder' body. This transfer of heat energy continues till both bodies attain the same degree of hotness (or) coldness. At this stage we say that the bodies have achieved 'Thermal equilibrium'.
* The state of thermal equilibrium denotes a state of a body where it neither receives nor gives out heat energy.
Temperature and Kinetic energy: Temperature of a body is an indicator of the average kinetic energy of molecules of that body.
* The average kinetic energy of the molecules is directly proportional to the absolute temperature.
Specific heat: The specific heat of a substance is the amount of heat required to raise the temperature of unit mass of the substance by one unit.
Method of mixtures Principle: When two or more bodies at different temperatures are brought into thermal contact, then net heat lost by the hot bodies is equal to net heat gained by cold bodies until they attain thermal equilibrium.

Net heat lost = Net heat gained

Internal energy of the system: The molecules of a system (body or substance) have different forms of energies such as linear Kinetic energy, rotational kinetic energy, vibrational energy and potential energy between molecules. The total energy of the system is called internal energy of the system.
Absolute temperature: Temperature measured on Kelvin scale is called absolute temperature.
Calorie: The C.G.S. unit of heat is Calorie (Cal). The amount of heat required to raise the temperature of 1 gram of water by 1° C is called Calorie.
Evaporation: "The process of escaping of molecules from the surface of a liquid at any temperature is called evaporation".
Condensation: Condensation is the phase change from gas to liquid.
Humidity: The amount of water vapour present in air is called humidity.
Dew: The water droplets condensed on surfaces of window - panes, flower, grass... etc are known as dew.
Fog: In the air the water molecules present in water vapour condense on the dust particles in the air and form small droplets of water. These droplets keep floating in the air and form a thick mist which restricts visibility. This thick mist is called fog.
Boiling: Boiling is a process in which the liquid phase changes to gaseous phase at a constant temperature at a given pressure. The temperature is called the boiling point of the liquid.
Melting: The process in which solid phase changes to liquid phase at a constant temperature is called melting. This constant temperature is called melting point.
Freezing: The process in which a substance in liquid phase changes to solid phase by loosing some of its energy is called freezing.
Latent heat of vapourization: The heat energy required to change 1 gram of liquid to gas at constant temperature is called latent heat of vapourization.
Joule: It is the unit of work and energy in S.I.
System: 1 Joule = 107 ergs = 0.2388 Calorie
Kinetic energy: It is the energy of motion. For a body of mass m, having a speed v, the kinetic energy is .
Celsius Scale of temperature: A temperature scale in which the fixed points are the temperatures at standard pressure of ice is equilibrium with water (0 °C) and water in equilibrium with steam (100 °C). The scale between these two temperatures, is divided into 100 degrees.
Kelvin scale of temperature: A temperature scale which has lower fixed point is 273.15 K and upper fixed point is 373.15 K. This is called Kelvin scale of temperature.
* For all practical purposes add 273 to the value of temperature is degree Celsius to get the temperature on the Kelvin scale.

Synopsis

* When heat energy flows out of your body you get the feeling of 'coldness' and when heat energy enters your body you get a feeling of 'hotness'.
* We say a metal piece is at a lower temperature as compared to a wooden piece when they are taken out of the fridge.
* When two bodies are placed in thermal contact, heat energy will be transferred from the 'hotter' body to the 'colder' body.
* This transfer of heat energy continues till both the bodies attain the same degree of hotness (or) coldness. At this stage, we say that the bodies have achieved 'thermal equilibrium'.
* If two different systems A and B in thermal contact, are in thermal equilibrium individually with another system C, than A and B are also in thermal equilibrium with each other.
* The S.I. Unit of heat is Joule (J) and C.G.S. unit is Calorie (Cal)
* 1 Cal = 4.186 Joules
* 0 °C = 273 K here Kelvin (K) is the S.I. unit of temperature.
* Bodies possess kinetic energy when they are in motion.
* Temperature determines direction of heat (energy) flow, where as heat is the energy that flows.
* When the same amount of heat is supplied to 50 grams of oil and 50 grams of water for the same time we observe that the rate of rise in temperature of the oil is higher than that of the rise in temperature of water.
* This means that the rate of rise in temperature depends upon the nature of the substance.
* We conclude that the specific heat of a substance depends upon its nature.
* When we supply heat energy to a system the heat energy given to it will be shared by the molecules among the various forms of energy.
* This sharing will vary from substance to substance.
* The rise in temperature is high for a substance if the maximum share of heat energy is utilised for increasing its linear kinetic energy.
* This sharing of heat energy of the system also varies with the temperature. That is why the specific heat is different for different substances.
* We can find how much heat (Q) is needed to rise the temperature of a certain mass (m) of the substance through certain degrees by using the equation Q = m S ∆ T. Where 's' is the specific heat of the substance.
* A Samosa appears to be cool outside but it is hot when we eat it. This is because the curry inside the Samosa contains ingradiants with higher specific heats.
* When two or more bodies at different temperatures are brought in to thermal contact, then the temperature (T) of the mixture is lower than the temperature of the hotter sample but higher than the temperature of the colder sample.
* This means that the hot sample has lost heat, and the cold sample has gained heat.
* If the initial temperatures of the samples of masses m1 and m2 be T1 and T2 (T1 > T2) than the temperature of the mixture T is given by

* When two or more bodies at different temperatures are brought into thermal contact then..
Net heat lost by the hot bodies = Net heat gained by the cold bodies
Until they attain thermal equilibrium it is supposed that no heat is lost by any other process.
* This is known as principle of method of mixtures.
* The specific heat of a substance is the amount of heat required to raise the temperature of unit mass of the substance by one unit.

* The process of escaping of molecules from the surface of a liquid at any temperature is called evaporation.
* Evaporation is a surface phenomenon.
* The change of phase from liquid to gas that occurs at the surface of the liquid is evaporation. We can define evaporation this way also.
* It is a cooling process, because the particles of liquid continuously give up their energy to the particles that are escaping from the surface.
* Rate of evaporation of a liquid depends on its surface area, temperature and the amount of vapour already present in the surrounding air.
* Air contains water molecules in the form of vapour.
* Condensation is 'The phase change from gas to liquid'. It is a warming process.
* You feel warm after you finish your bath under the shower on a hot day. This is due to condensation of vapour molecules surrounding you on your skin. This makes you feel warm.
* Some water vapour is always present in air surrounding us. This vapour may come from evaporation of water from the surface of rivers, lakes, ponds and from the drying of wet clothes, sweat and so on.
* The presence of water vapour molecules in air is said to make the atmosphere humid. The amount of water vapour present in air is called humidity.
* In early morning during winter we notice that water droplets from on window pans, flowers, grass... etc. The water droplets condensed on such surfaces are known as dew.
* The whole atmosphere in any region contains a large amount of water vapour. The water molecules present in the vapour condense on the dust particles in air and form small droplets of water. These droplets keep floating in the air and form a thick mist which restrict visibility. This thick mist is called fog.
* 'Boiling is a process in which the liquid phase changes to gaseous phase at a constant temperature at a given pressure'. This temperature is called boiling point of the liquid.
* Evaporation takes place at any temperature while boiling occurs at a definite temperature called the boiling point.
* The heat energy required to change 1 gm of liquid to gas at constant temperature is called latent heat of vapourization.
* The latent heat of vapourization L = Q/m, where m is the mass of the liquid which requires heat energy Q calories to change from its state from liquid phase to gas phase.
* C.G.S. unit of latent heat of vapourization is Cal / gm and S.I. unit is J/Kg.
* The process in which solid phase changes to liquid phase at a constant temperature is called melting. This constant temperature is called melting point.
* Heat energy required to convert 1 gm of solid completely in to liquid at constant temperature is called latent heat of fusion.
* The heat required to change 1 gm of solid into liquid is

= L (Latent heat of fusion). Here Q is the amount of heat required to change 'm' gram of solid in to liquid.
* The value of lalent heat of fusion of ice L =
* When water is kept in a refrigerator it converts in to solid ice. It means that during the process of conversion from liquid to solid, the internal energy of water decreases, so that it becomes solid ice. This process is called freezing.
* The density of ice is less than that of water. So ice floats on water.
* Water expands on freezing.

(Writer: C.V.Sarveswara Sarma)

Posted Date : 28-05-2021

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.