1. محاضرة رقم 4 Thermodynamics Temperature and Ideal Gases Thermal contact Thermal contact between two objects is if it is possible to exchange thermal energy without do work.

2. Thermal equilibrium Thermal equilibrium is achieved when two objects or systems reach the same temperature and cease to exchange energy through heat. When two objects are placed together, the object with more heat energy will lose that energy to the object with less heat energy. Eventually, their temperatures will be equal and they will cease to exchange heat energy as neither object is warmer or cooler than the other. At this point, they are in a state of thermal equilibrium Thermal equilibrium between two objects occurs if the thermal contact between them, as well as the net heat exchange between them is equal to zero

4. The zeroth law of thermodynamics The "zeroth law" states that if two systems are at the same time in thermal equilibrium with a third system, they are in thermal equilibrium with each other.thermal equilibrium

5. Thermometer A thermometer is a device that measures the temperature of things. The name is made up of two smaller words: "Thermo" means heat and "meter" means to measure. You can use a thermometer to tell the temperature outside or inside your house, inside your oven, even the temperature of your body if you're sick. When you look at a regular outside bulb thermometer, you'll see a thin red or sil ver line that grows longer when it is hotter. The line goes down in cold weather. This liquid is sometimes colored alcohol but can also be a metallic liquid called mercury. Both mercury and alcohol grow bigger when heated and smaller when cooled. Inside the glass tube of a thermometer, the liquid has no place to go but up when the temperature is hot and down when the temperature is cold. Thermometer works through a change in the physical properties of the temperature change, such as property of extended objects with increasing temperature, change in pressure, change in electrical resistance of a wire with temperature change.

6. Here we mention the different types of thermometer Type of thermometer نوع الثيرمومتر Material المادة Physical property الكمية الفيزيائية (1) Liquid thermometerMercury or AlcoholChange in length (2) Gas ThermometerHydrogenChange in pressure (3) Resistance thermometerPlatinumChange in resistance (4) Thermocouple thermometerChromel and Alumel Change in electric potential (5) Radiation ThermometerPyrometer Change in radiation colour (6) Magnetic thermometer Change in susceptibility

7. Celsius scale Metric scale in which the temperature range between the freezing point (zero degree Celsius or 0°C) and the boiling point (one hundred degrees Celsius or 100°C) of water is divided into 100 equal fractions (degrees). Formerly known as Centigrade scale, it is named after the Swedish astronomer Anders Celsius (1701-44) who in 1742 invented the inverted form of this scale.scale temperaturerangefreezing pointboiling pointdegreesfractionsform

8. Fahrenheit scale temperature scale used in the English-speaking world and parts of Europe, 18 th – 21 st centuries, having the melting point of ice at 32 degrees and the boiling point of water at 212 degrees.

9. Kelvin scale

10. Comparison of Temperature Scales Set PointsFahrenheitCelsiusKelvin water boils212100373 body temperature 98.637310 water freezes320273 absolute zero-460-2730 Temperature Conversion Formulas ConversionFormulaExample Celsius to Kelvin K = C + 27321 o C = 294 K Kelvin to Celsius C = K - 273313 K = 40 o C Fahrenheit to Celsius C = (F - 32) x 5/989 o F = 31.7 o C Celsius to Fahrenheit F = (C x 9/5) + 3250 o C = 122 o F

11. Example

13. Thermal expansion of solids and Liquids When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is limited in size, and only occurs within limited temperature ranges (see examples below). The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion and generally varies with temperature.

14. Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. [1]volumetemperature [1]

15. coefficient of linear expansion The linear thermal expansion coefficient relates the change in a material's linear dimensions to a change in temperature. It is the fractional change in length per degree of temperature change.

17.  Coefficient of volume expansion Is equivalent to three times the coefficient of linear expansion of materials similar  = 3 

18. Example

19. The Expansion of Water Upon Freezing Generally liquids expand and increase in size with increasing temperature, and the coefficient of volumetric is ten times greater for solids. But in the case of water the density increases with temperature from 0 to 4 ° C, and if the temperature has increased more than 4 degrees Celsius, the water expands, up تكون كثافة الماء اكبر ما يمكن عند درجة حرارة 4 o C وتساوي 1000Kg/m 3.

20. Maximum density of water is 1000 kg/m 3 at 4 º C Density of ice = 917 kg/m 3.... Ice floats! These properties of water have important consequences in its role in the ecosystem of Earth. Water at a temperature of 4 °C will always accumulate at the bottom of fresh water lakes, irrespective of the temperature in the atmosphere. Since water and ice are poor conductors of heat [23] (good insulators) it is unlikely that sufficiently deep lakes will freeze completely, unless stirred by strong currents that mix cooler and warmer water and accelerate the cooling. In warming weather, chunks of ice float, rather than sink to the bottom where they might melt extremely slowly. These phenomena thus may help to preserve aquatic lifeecosystem [23]