Physics notes for class 11 NCERT/CBSE, Study notes of Physics

Download Physics notes for class 11 NCERT/CBSE and more Study notes Physics in PDF only on Docsity! 1 | P a g e www.ncerthelp.com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more) Physics Notes Class 11 CHAPTER 12 THERMODYNAMICS The branch dealing with measurement of temperature is called thremometry and the devices used to measure temperature are called thermometers. Heat Heat is a form of energy called thermal energy which flows from a higher temperature body to a lower temperature body when they are placed in contact. Heat or thermal energy of a body is the sum of kinetic energies of all its constituent particles, on account of translational, vibrational and rotational motion. The SI unit of heat energy is joule (J). The practical unit of heat energy is calorie. 1 cal = 4.18 J 1 calorie is the quantity of heat required to raise the temperature of 1 g of water by 1°C. Mechanical energy or work (W) can be converted into heat (Q) by 1 W = JQ where J = Joule’s mechanical equivalent of heat. J is a conversion factor (not a physical quantity) and its value is 4.186 J/cal. Temperature Temperature of a body is the degree of hotness or coldness of the body. A device which is used to measure the temperature, is called a thermometer. Highest possible temperature achieved in laboratory is about 108 while lowest possible temperature attained is 10-8 K. Branch of Physics dealing with production and measurement temperature close to 0 K is known as cryagenics, while that deaf with the measurement of very high temperature is called pyromet Temperature of the core of the sun is 107 K while that of its surface 6000 K. NTP or STP implies 273.15 K (0°C = 32°F). Different Scale of Temperature 2 | P a g e www.ncerthelp.com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more) 1. Celsius Scale In this scale of temperature, the melting point ice is taken as 0°C and the boiling point of water as 100°C and space between these two points is divided into 100 equal parts 2. Fahrenheit Scale In this scale of temperature, the melt point of ice is taken as 32°F and the boiling point of water as 211 and the space between these two points is divided into 180 equal parts. 3. Kelvin Scale In this scale of temperature, the melting pouxl ice is taken as 273 K and the boiling point of water as 373 K the space between these two points is divided into 100 equal pss Relation between Different Scales of Temperatures Thermometric Property The property of an object which changes with temperature, is call thermometric property. Different thermometric properties thermometers have been given below (i) Pressure of a Gas at Constant Volume where p, p100. and pt, are pressure of a gas at constant volume 0°C, 100°C and t°C. A constant volume gas thermometer can measure tempera from – 200°C to 500°C. (ii) Electrical Resistance of Metals Rt = R0(1 + αt + βt2) where α and β are constants for a metal. As β is too small therefore we can take Rt = R0(1 + αt) 5 | P a g e www.ncerthelp.com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)  where, m = mass of the substance,  c = specific heat of the substance and  Δt = change in temperature. Thermal (Heat) Capacity Heat capacity of any body is equal to the amount of heat energy required to increase its temperature through 1°C. Heat capacity = me where c = specific heat of the substance of the body and m = mass of the body. Its SI unit is joule/kelvin (J/K). Water Equivalent It is the quantity of water whose thermal capacity is same as the heat capacity of the body. It is denoted by W. W = ms = heat capacity of the body. Latent Heat The heat energy absorbed or released at constant temperature per unit mass for change of state is called latent heat. Heat energy absorbed or released during change of state is given by Q = mL where m = mass of the substance and L = latent heat. Its unit is cal/g or J/kg and its dimension is [L2T-2]. For water at its normal boiling point or condensation temperature (100°C), the latent heat of vaporisation is L = 540 cal/g = 40.8 kJ/ mol = 2260 kJ/kg For water at its normal freezing temperature or melting point (0°C), the latent heat of fusion is L = 80 cal/ g = 60 kJ/mol = 336 kJ/kg 6 | P a g e www.ncerthelp.com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more) It is more painful to get burnt by steam rather than by boiling was 100°C gets converted to water at 100°C, then it gives out 536 heat. So, it is clear that steam at 100°C has more heat than wat 100°C (i.e., boiling of water). After snow falls, the temperature of the atmosphere becomes very This is because the snow absorbs the heat from the atmosphere to down. So, in the mountains, when snow falls, one does not feel too but when ice melts, he feels too cold. There is more shivering effect of ice cream on teeth as compare that of water (obtained from ice). This is because when ice cream down, it absorbs large amount of heat from teeth. Melting Conversion of solid into liquid state at constant temperature is melting. Evaporation Conversion of liquid into vapour at all temperatures (even below boiling point) is called evaporation. Boiling When a liquid is heated gradually, at a particular temperature saturated vapour pressure of the liquid becomes equal to atmospheric pressure, now bubbles of vapour rise to the surface d liquid. This process is called boiling of the liquid. The temperature at which a liquid boils, is called boiling point The boiling point of water increases with increase in pre sure decreases with decrease in pressure. Sublimation The conversion of a solid into vapour state is called sublimation. Hoar Frost The conversion of vapours into solid state is called hoar fr.. Calorimetry This is the branch of heat transfer that deals with the measorette heat. The heat is usually measured in calories or kilo calories. Principle of Calorimetry When a hot body is mixed with a cold body, then heat lost by ha is equal to the heat gained by cold body. 7 | P a g e www.ncerthelp.com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more) Heat lost = Heat gain Thermal Expansion Increase in size on heating is called thermal expansion. There are three types of thermal expansion. 1. Expansion of solids 2. Expansion of liquids 3. Expansion of gases Expansion of Solids Three types of expansion -takes place in solid. Linear Expansion Expansion in length on heating is called linear expansion. Increase in length l2 = l1(1 + α Δt) where, ll and l2 are initial and final lengths,Δt = change in temperature and α = coefficient of linear expansion. Coefficient of linear expansion α = (Δl/l * Δt) where 1= real length and Δl = change in length and Δt= change in temperature. Superficial Expansion Expansion in area on heating is called superficial expansion. Increase in area A2 = A1(1 + β Δt) where, A1 and A2 are initial and final areas and β is a coefficient of superficial expansion. Coefficient of superficial expansion β = (ΔA/A * Δt) where. A = area, AA = change in area and At = change in temperature. Cubical Expansion Expansion in volume on heating is called cubical expansion. Increase in volume V2 = V1(1 + γΔt)