Tiêu đề 11-Thermal-Properties-of-Matter-f.pdf ✅

Physics Smart Booklet 1 11.Thermal Properties of Matter Physics Smart Booklet Theory + NCERT MCQs + Topic Wise Practice MCQs + NEET PYQs ©
Physics Smart Booklet 2
Physics Smart Booklet 3 THERMAL PROPERTIES OF MATTER Heat and Temperature Heat, temperature and thermal equilibrium The energy transferred from a hot body to a cold body is called heat. Thus “heat is energy in transit”. Temperature is an index of hotness or coldness of a body and it determines the direction of heat flow. Heat flows from a body at a higher temperature to a body at a lower temperature. Two bodies are said to be in thermal equilibrium if no net transfer of heat takes place when they are placed in thermal contact. Then two bodies are at the same temperature. Zeroth law of thermodynamics Statement: If two bodies are in thermal equilibrium with a third body, then those two bodies are in thermal equilibrium with each other. Thus, temperature is a thermal property which has the same value in all bodies which are in thermal equilibrium. Thermometry A device used to measure the temperature of a body is called a thermometer. The linear variation of some physical property of a substance with change in temperature is the principle of a thermometer. For example, following properties are used in different thermometer. • The property of increase in volume of a gas (at constant pressure) or increase in pressure of a gas (at constant volume) with increase in temperature is used in gas thermometers. • The property of expansion of liquids on heating is used in mercury thermometer. • The property of increase in resistance with increase in temperature is used in resistance thermometers. Depending upon the range of measurement of temperature, the following thermometers are also used: 1. Thermoelectric thermometers 2. Radiation thermometer (Pyrometers) 3. Bimetalic strip thermometers Temperature scales Different scales are employed to measure temperature. Each scale is characterized by its own set of lower fixed point and upper fixed points. Scale Lower fixed point Upper fixed point Celsius (centigrade) 0 C 100 C Fahrenheit 32 C 212 C Kelvin 273.15 K 373.15 K If the temperature of a body on Celsius, Fahrenheit and Kelvin scale is recorded as C, F and K respectively, then, 100 N K 273 180 F 32 100 C 0  − 0 = − = − = − where , 0 and N represent corresponding temperature, lower fixed point and number of divisions on some new scale. In general, the temperature corresponding to any length l of the mercury column can be obtained using the formula t 100 100 0 0  − − = l l l l where l0 and l100 denote the lengths of the mercury column at 0 C and 100 C respectively.
Physics Smart Booklet 4 The triple point of water By international agreement, the triple point of water is selected as the standard fixed-point temperature for the calibration of thermometers. Triple point is a state in which ice, water and water vapour can stay together in equilibrium. Triple point of water has been assigned a value of 273.16 K.  In constant volume gas thermometers, the temperature of the gas when pressure is p is obtained by using the equation tr p T 273.16 p =  where ptr is the pressure at triple point of water. Illustrations 1. At what temperature, does the following pair of scales give the same reading? Celsius and Fahrenheit. (A) – 60 (B) – 30 (C) – 50 (D) – 40 Ans (D) Let the required reading be . Then C 0 F 32 0 32 40 100 180 100 180  −  −  −  − =  =  −  −  = −  40 C 40 F 2. In a scientific book that describes a temperature called Y, boiling and freezing point of water are referred as 65 Y and – 15 Y respectively. To what temperature on Fahrenheit scale would a temperature –95Y correspond? (A) – 148 F (B) – 158 F (C) – 128 F (D) – 138 F Ans (A) F 32 Y ( 15) 212 32 65 ( 15)  −  − − = − − − Putting – 95 Y in place of Y in the equation and solving for F gives the answer – 148 F 3. Why does a doctor taking your body temperature wait for the thermometer reading to stop changing before recording it? Ans It takes a while before the thermometer is in equilibrium with your body. At that stage, the thermometer reading corresponds to your body temperature. 4. Does a thermometer read the temperature of its body or that of some other object? Ans It reads its own temperature; however when it is in thermal equilibrium with the surrounding, we also get the temperature of the surroundings. 5. The fundamental interval (that is the number of divisions between the lower fixed point and the upper fixed point) on the two scales X and Y are 50 and 150, respectively. The ice point on both the scales is at 0°. If the temperature on the X-scale is 15°, the temperature on the Y-scale is (A) 30° (B) 45° (C) 60° (D) 75° Ans (B) 150 y 0 50 x 0 − = − If x = 15°, then y = 45°