HEAT 1.pptx heat class 10th icse physics

Heat class 12 state board karnataka...

1. 5. HEAT HEAT CAPACITY, SPECIFIC HEAT CAPACITY AND ITS MEASUREMENT

2. Calorimetry : meaning , specific heat capacity; principle of method of mixtures; Numerical Problems on specific heat capacity using heat loss and gain and the method of mixtures. Heat and its units (calorie, joule), temperature and its units ( o C , , K); thermal (heat) capacity C' = Q/T... (SI unit of C'): Specific heat Capacity C = Q/ mT (SI unit of C) Mutual relation between Heat Capacity and Specific Heat capacity, values of C for some common substances (ice, water and copper). Principle of method of mixtures including mathematical statement. Natural phenomenon involving specific heat. Consequences of high specific heat of water. [Simple numerical problems].

3. Heat (Q) Each substance is made up of molecules . The molecules in a substance are in a state of random motion. The kinetic energy due to random motion of the molecules of a substance is known as its heat energy. Thus each body possesses heat energy inform of its internal kinetic energy. When some quantity of heat is supplied to a body, the random molecular motion increases, which results in the increase in average internal kinetic energy of its molecules and hence the increase in its temperature. Similarly, if some quantity of heat is removed (or withdrawn) from a body, its random molecular motion decreases so the average internal kinetic energy of the body decreases and the temperature of the body falls. Thus the average internal kinetic energy of the molecules of a substance is a measure of temperature of that substance . Temperature

4. Heat Temperature Heat is a form of energy that can transfer from a hot body to a cold body. Temperature is the degree of hotness and coldness of a body. Heat is the total kinetic energy and potential energy obtained by molecules in an object. Temperature is the average K.E of molecules in a substance. Heat flows from hot body to cold body. It rises when heated and falls down when an object is cooled down. It has a working ability. It does not have the working ability. Its SI unit is “Joule”. Its SI unit is “Kelvin”. It is measured by the calorimeter. It is measured by the thermometer. It is represented by “Q”. It is represented by “T”.

5. HEAT UNIT CGS SI Calorie(cal) joule(J) Calorie : The heat energy required to raise the temperature of 1 g  of water through 1 C is known as calorie  1 calorie = 4.18(4.2 ) J 1 kilocalorie =1000cal or 4186 J

6. HEAT (OR THERMAL) CAPACITY (C' = Q/∆T) The heat capacity of a body is the amount of heat energy required to raise its temperature by 1 C or 1 K ‘ Units of heat capacity S.l . : joule per kelvin (or J k -1 ) (or) joule per degree C (or J c -I ).   The other common units of heat capacity are calorie c -I (or cal k -1 ) and kilo-calorie c -I (or kilo-calorie k -1 ).

7. SPECIFIC HEAT CAPACITY (c) Heat capacity of a body when expressed for unit mass is called its specific heat capacity. It is denoted by the symbol c. Thus the specific heat capacity of a substance (or a body) is defined as the heat capacity per unit mass of that body i.e., 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 1 c (or 1K). Units of specific heat capacity S.I. unit of specific heat capacity is joule per kilogramme per kelvin ( or J kg -I K -l ) or joule per kilogramme per degree celsius (or J kg -I c -I ). The other units of specific heat capacity are cal g -l c -I I and kilo-cal kg -I c -I .  

8. Specific heat capacity of some common substances The specific heat capacity of a substance is its characteristic property. It is different for different substances. If we heat equal masses of two different substances on the same burner so that the rate of heat supply is same, we notice that after the same time interval, the rise in temperature for the two substances is different. This is due to their different specific heat capacities. Water has an unusually high specific heat capacity (= 4200 J kg -I K -l ) The specific heat capacity is maximum for hydrogen (c = 14630 J kg -I K -l ).

9. RELATION BETWEEN HEAT CAPACITY AND SPECIFIC HEAT CAPACITY Q =m c ∆ T C ’ = Q / ∆ T C = Q/ m ∆ T C = C ’ / m C ’ = c m Heat capacity = specific heat capacity * mass

10. PRINCIPLE OF MIXTURES (OR PRINCIPLE OF CALORIMETRY) The principle of measurement of heat is based on the law of conservation of energy. When a hot body is mixed (or is kept in contact) with a cold body, heat energy passes from the hot body to the cold body, till both the bodies attain the same temperature. If no heat energy is exchanged with the surroundings, i.e., if the system is fully insulated, then Heat energy lost by the hot body= Heat energy gained by the cold body This is called the principle of mixtures or the principle of calorimetry . 

11. Let a substance A of mass m l , specific heat capacity C 1 and at a higher temperature T l be mixed with another substance B of mass m 2 , specific heat capacity c 2 and at a lower temperature T 2 (i.e., T 2 < T 1 ). If the final temperature of mixture becomes T, then Fall in temperature of substance A = T 1 — T Rise in temperature of substance B = T — T 2 Heat energy lost by A = m l x C l x fall in temperature = = m l x C l x (T 1 — T) ----------( i ) Heat energy gained by B = m 2 x c 2 x rise in temperature = m 2 x c 2 x(T — T 2 ) ----------- (ii) If no heat energy is lost to the surroundings, then by the principle of mixtures , Heat energy lost by A = Heat energy gained by B m l x C l x (T 1 — T) = m 2 x c 2 x(T — T 2 )

12. NATURAL  PHENOMENA AND CONSEQUENCES OF HIGH SPECIFIC HEAT CAPACITY OF WATER Similarly, a certain mass of water will give out nearly five times more heat energy than that given by the same mass of sand for the same fall in temperature. As such, sand (or earth) gets heated or cooled more rapidly as compared to water under the similar conditions. Thus, a large difference in temperature is developed between the land and the sea due to which land and sea breezes are formed*. These breezes make the climate near the seashore moderate. ( i ) The climate near the seashore is moderate: The specific heat capacity of water is very high 1000 cal kg-I o c -l or 4200 J kg -1 k -1 ). It is about five times as high as that of sand. Hence the heat energy required for the same rise in temperature by a certain mass of water will be nearly five times than that required by the same mass of sand.

13. Hot water bottles are used for fomentation : 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 longer period.

14. Water is used as an effective coolant : By allowing water to flow in pipes around the heated parts of a machine, heat energy from such parts is removed (e.g. radiators in car and generator are filled with water). Water in pipes extracts more heat from surroundings without much rise in its temperature because of its large specific heat capacity. 

15. In cold countries, water is used as heat reservoir for wine and juice bottles to avoid their freezing : The reason is that water due to its high specific heat capacity can impart a large amount of heat before reaching up to the freezing temperature. Hence bottles kept in water remain warm and they do not freeze even when the surrounding temperature falls considerab ly

16. (v) Farmers fill their fields with water to protect the crops from frost : In the absence of water, if on a cold winter night, the atmospheric temperature falls below O O C, the water in the fine capillaries of plants will freeze, so the veins will burst due to the increase in volume of water on freezing. As a result, plants will die and the crop will be destroyed. In order to save crop on such cold nights, farmers fill their fields with water because water has a high specific heat capacity, so it does not allow the temperature in the surrounding area of plants to fall up to O O C

17. All plants and animals have a high content of water in their bodies : All plants and animals have nearly 80% to 90% of water in their bodies. This water, because of its high specific heat capacity, helps in maintaining their body temperature nearly same in all seasons.