Thermal Physics (Thermodynamics) Zeroth Law of Thermodynamics Zeroth Law of Thermodynamics Thermometers Temperature Scales

Thermal Physics (Thermodynamics) Zeroth Law of Thermodynamics Zeroth Law of Thermodynamics Thermometers Temperature Scales www.phwiki.com

Thermal Physics (Thermodynamics) Zeroth Law of Thermodynamics Zeroth Law of Thermodynamics Thermometers Temperature Scales

Wrenn, Lisa, Features Editor has reference to this Academic Journal, PHwiki organized this Journal Thermal Physics (Thermodynamics) Concerned with the concepts of thermal (or internal) energy transfers between a system in addition to its environment in addition to the resulting temperature variations Temperature is central concept of thermodynamics Be careful not to trust your (subjective) senses to measure temperature! Historically, the development of thermodynamics paralleled the development of atomic theory Concerns itself with the physical in addition to chemical trans as long as mations of matter in all of its as long as ms: solid, liquid, in addition to gas Temperature, heat flow, in addition to internal energies will be studied Zeroth Law of Thermodynamics The flow of energy that occurs between 2 objects or systems due to a temperature difference between them is called heat flow Objects are in thermal contact if heat flow can take place between them Thermal equilibrium exists when two objects in thermal contact with each other cease to exchange energy Definition of temperature relies on the zeroth law of thermodynamics: If objects A in addition to B are in thermal equilibrium with a third object, C, then A in addition to B are in thermal contact with each other Zeroth Law of Thermodynamics Less as long as mal definition: Every body has a property called temperature. When 2 bodies are in thermal equilibrium, their temperatures are equal, in addition to vice versa Zeroth law used constantly in the lab If we want to know if 2 liquids have same temperature, we measure temperature of each with a thermometer No need to bring them into thermal contact Zeroth law came to light only in 1930s, long after 1st in addition to 2nd laws of thermodynamics were established

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Thermometers Thermometers are devices used to measure the temperature of an object or a system Example is mercury thermometer Make use of physical properties that change with temperature Many physical properties can be used volume of a liquid length of a solid pressure of a gas held at constant volume volume of a gas held at constant pressure electric resistance of a conductor color of a very hot object Temperature Scales Thermometers can be calibrated by placing them in thermal contact with an environment that remains at constant temperature Environment could be mixture of ice in addition to water in thermal equilibrium Also commonly used is water in addition to steam in thermal equilibrium An ear thermometer measures infrared radiation from the eardrum – why is this useful Celsius scale: Temp. of ice–water (water–steam) mixture defined as 0°C (100°C) Freezing point vs. boiling point of water Distance between these 2 points divided into 100 equal segments Temperature Scales Fahrenheit scale: Most common scale used in the U.S. Employs a smaller degree than Celsius scale Uses a different zero of temperature than Celsius scale Temperature of the freezing point of water is set at 32°F Temperature of the boiling point of water is set at 212°F 180 divisions between these 2 points Conversion between Celsius (TC) in addition to Fahrenheit (TF) temperatures:

Gas Thermometer Ideally, the readings of a thermometer should not depend on material used Gas thermometer comes close to this ideal Principle is that pressure of a gas at constant volume increases with temperature Gas placed in constant-volume container in addition to pressure is measured (manometer in figure above) Calibrated by measuring pressure at 2 temperatures Temperature readings are nearly independent of the gas Pressure varies with temperature when maintaining a constant volume Gas Thermometer If temperature measurements are per as long as med with gas in flask at different starting pressures at 0°C, the data looks like the graph at right: In each case, regardless of the gas used, the curves extrapolate to the same temperature (absolute zero) at zero pressure Gases liquefy in addition to solidify at very low temperatures, so we can’t actually observe this zero-pressure condition The absolute-zero reference point as long as ms basis of Kelvin temperature scale Kelvin Temperature Scale Named as long as British physicist Lord Kelvin (1824–1907) Units same as those on Celsius scale, but zero point is shifted so that 0 K = –273.15°C: Modern definition (since 1954) of Kelvin scale defined in terms of two points First point is absolute zero Second point is the triple point of water Triple point is the single point where water can exist as solid, liquid, in addition to gas Single temperature in addition to pressure Occurs at 0.01°C in addition to P = 4.58 mm Hg 1 K = 1/273.16 of temperature of triple point of water

Some Kelvin Temperatures in addition to Temperature Scale Comparisons Thermal Expansion The thermal expansion of an object is a consequence of the change in the average separation between its constituent atoms or molecules At ordinary temperatures, molecules vibrate with a small amplitude As temperature increases, the amplitude increases This causes the overall object as a whole to exp in addition to For relatively small changes in temperature, the linear dimensions of object change according to: Coefficient of linear expansion, a, depends on the material (see Table 10.1) These are average coefficients (they can vary with temperature) Thermal Expansion Since the linear dimensions of an object change with temperature, there is also a change in surface area: And a change in volume: g = 2a in addition to b = 3a only if a is the same in all directions Many applications of thermal expansion Pyrex glass Expansion joints in bridges in addition to buildings Rising sea levels due to ocean warming (g = 2a = coefficient of area expansion) (b = 3a = coefficient of volume expansion as long as solids; as long as fluids, see Table 10.1)

Thermal Expansion Thermostats Bimetallic strips in thermostats (2 metals exp in addition to differently) (abrass > asteel) CQ1: The Statue of Liberty is 93 m tall on a summer morning when the temperature is 20°C. If the temperature of the statue rises from 20°C to 30°C, what is the order of magnitude of the statue’s increase in height Choose the best estimate, treating the statue as though it were solid copper (a = 17 × 10–6 °C–1 ). 0.1 mm 1 mm 1 cm 10 cm 1 m Example Problem 10.23 Solution (details given in class): 2.7 102 N The b in addition to in the figure at right is stainless steel (coefficient of linear expansion a = 17.3 10–6 °C–1 ; Young’s modulus Y = 18 1010 N/m2). It is essentially circular with an initial mean radius of 5.0 mm, a height of 4.0 mm, in addition to a thickness of 0.50 mm. If the b in addition to just fits snugly over the tooth when heated to a temperature of 80°C, what is the tension in the b in addition to when it cools to a temperature of 37°C

Thermal Expansion of Water As the temperature of water decreases from 4ºC to 0ºC, it exp in addition to s in addition to its density decreases Above 4ºC, water exp in addition to s with increasing temperature, typical of other liquids in addition to materials Maximum density of water is 1000 kg/m3 at 4ºC This unusual behavior explains why: ice humps up in the middle of the compartments in an ice cube tray a lake freezes slowly from the top down (important as long as animal in addition to plant life!) water pipes can burst in the winter Ideal Gas A gas does not have a fixed volume or pressure In a container, the gas exp in addition to s to fill the container Most gases at room temperature in addition to pressure behave approximately as an ideal gas (one in which there is simple relationship between P, V, in addition to T) Characteristics of ideal gas: Collection of atoms or molecules that move r in addition to omly Exert no long-range as long as ce on one another Occupy a negligible fraction of the volume of their container Underst in addition to ing ideal gases is useful because all real gases approach an ideal gas at low enough densities (when molecules are far enough apart that they do not interact with each other) Ideal Gas It’s convenient to express the amount of gas in a given volume in terms of the number of moles, n: One mole is the amount of the substance that contains as many atoms as there are atoms in 12 g of the carbon–12 isotope 1 mol of a substance contains the same number of atoms as in 1 mol of any other substance The number of atoms in one mole is called Avogadro’s Number = NA = 6.02 1023 atoms/mol We can use this number to calculate the mass of an individual atom:

Ideal Gas Law Boyle’s Law At a constant temperature, pressure is inversely proportional to the volume Charles’ Law At a constant pressure, the temperature is directly proportional to the volume Gay-Lussac’s Law Ideal Gas Properties At a constant volume, the pressure is directly proportional to the temperature These 3 laws are summarized by the Ideal Gas Law: R = universal gas constant = 8.31 J/molK = 0.0821 Latm/molK (P = absolute pressure, T = temp. in Kelvin) (note that if n = constant, PV/T = constant) CQ2: If the volume of an ideal gas is doubled while its temperature is quadrupled, what happens to the pressure of the gas It remains the same. It decreases by a factor of 2. It decreases by a factor of 4. It increases by a factor of 2. It increases by a factor of 4. Example Problem 10.32 Solution (details given in class): 884 balloons A tank having a volume of 0.100 m3 contains helium gas at 150 atm. How many balloons can the tank blow up if each filled balloon is a sphere 0.300 m in diameter at an absolute pressure of 1.20 atm

CQ3: Interactive Example Problem 10.35 A weather balloon is designed to exp in addition to to a maximum radius of 20 m at its working altitude, where the air pressure is 0.030 atm in addition to the temperature is 200 K. If the balloon is filled at atmospheric pressure in addition to 300 K, what is its radius at liftoff 4.2 m 7.1 m 18 m 49 m 358 m

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