424013676-Thermal-Physics-Thermal-Physics-Thermal-Physics-Thermal-Physics

424013676-Thermal-Physics-Thermal-Physics-Thermal-Physics-Thermal-Physics

1. THERMAL PHYSICS A LEVELS

2. INTERNAL ENERGY Sum of random distribution of KE and PE of its atoms or molecules in a given system. Includes kinetic and potential energy associated with the random translational, rotational and vibrational motion of the atoms or molecules. Also includes any potential energy bonding the particles together. For any matter (in any of the three phases), the molecules have different KE and PE.

3. INTERNAL ENERGY First Law of Thermodynamics Increase in internal energy is always the sum of the energy supplied by heating and the energy supplied by doing work. Energy is always conserved. Δ U = Q + W Q is the energy transferred to the system by heat W is the work done by the system ΔU is the change in internal energy

4. INTERNAL ENERGY CHANGING INTERNAL ENERGY By doing work Requires a macroscopic displacement of an object through the application of a force By heat Occurs through the random molecular collisions

5. TEMPERATURE Temperature is the degree of sensible heat or cold, expressed in terms of a specific scale . Tells us about direction in which energy flows. Always flows from a region of higher temperature to a region of lower temperature known as T hermal Energy. Thermal equilibrium – No net transfer of thermal energy.

6. TEMPERATURE Thermal equilibrium If a body (X) at a higher temperature is in contact with a body (Y) at a lower temperature, then X will transfer heat energy to the lower temperature object ( Y) This process will continue till the objects attain the same temperature. The temperature of both objects will become same. This thermal state in which both bodies are at the same temp is called thermal equilibrium.

7. TEMPERATURE Temperature Scale Several scales and units exist for measuring temperature, the most common being Celsius, Fahrenheit, and especially in science Kelvin.

8. TEMPERATURE Celsius Scale The Celsius scale is used for common temperature measurements in most of the world. It is an empirical scale. Its zero point is 0°C being defined by the freezing point (melting point) of pure water, and 100°C was the boiling point of pure water , both at sea level atmospheric pressure. Because of the hundred degree interval, it is called a centigrade scale.

9. TEMPERATURE Fahrenheit Scale The United States commonly uses the Fahrenheit scale, on which water freezes at 32°F and boils at 212°F at sea level atmospheric pressure.

10. TEMPERATURE Kelvin Scale Many scientific measurements use the Kelvin temperature scale. It is a thermodynamic or absolute temperature scale. Its zero point 0K, is defined to coincide with coldest physically-possible temperature. The temperature of absolute zero occurs at 0K = - 273.15°C and the freezing point of water at sea level atmospheric pressure occurs at 273.15K = 0°C .

11. TEMPERATURE Comparison between different scales of temperature

12. TEMPERATURE ABSOLUTE TEMPERATURE measured in units of Kelvin (K) where 0 K is absolute zero (at which a gas has zero pressure) No possibility to have a temperature less than 0K. Matter has no energy left in it.

13. TEMPERATURE Kelvin Scale (Advantages) Not defined in terms of a property of any particular substance Based on the fact that the average KE increases with increase in temperature and is same for all substances at a particular temperature. Doesn’t depend on material itself.

14. TEMPERATURE Triple Point of water The temperature at which Ice, water and water vapour can co-exist, which is defined as 273.15 K = 0.01°C Gap between Absolute 0K and triple point of water is divided into 273.15 divisions. Each division = 1K 1 degree change in Celsius = 1 degree change in Kelvin   https://www.youtube.com/watch?v=Juz9pVVsmQQ

15. THERMOMETERS Device used to measure temperature. Thermometric properties Length varies linearly with temperature Used in liquid-in-glass thermometers Pressure varies linearly with temperature Used in constant volume gas thermometers Volume varies linearly with temperature Used in constant pressure gas thermometers Resistance varies linearly with temp Used platinum resistance thermometers

16. THERMOMETERS Definitions to remember The physical property on which a particular thermometer is based is called the thermometric property . Thermometric substance is the material used in the thermometer, whose property varies with temperature. Thermometric property should vary linearly with temperature over a reasonable range of temperature. The range of linearity of the thermometric property is called the thermometric range .

17. THERMOMETERS Factors to consider while choosing a thermometer Accuracy Sensitivity (distance between divisions on the scale) Range of temperatures it can measure Speed of response – measure rapidly varying temperatures Sensitive part of the thermometer should be small so that it does not absorb much heat from the object It should be easy to read – no complicated calibrations / settings

18. THERMOMETERS Platinum Wire Thermometers These are based on the variation of electrical resistance due to temperature Resistance of a metal wire increases with increase in temperature. Range of temperature they can measure is from -260 °C to 1700 °C Temp sensor or material is a coil of fine platinum wire Advantages of platinum resistance thermometers: High accuracy Low drift Wide operating range Disadvantages of Platinum Thermometers Not very sensitive to small changes in temp Slow response time

19. Thermistor A thermistor is a type of resistor whose resistance changes with temperature Semiconductors are used in these devices The electrical resistance decreases very rapidly with increasing temperature. Thus , we say that thermistors have a negative temperature coefficient of resistance Advantages of thermistors: Sensitivity is high Their size is very small – hence can be used to measure temperature of small objects Disadvantages of Thermistors Their scale is non-linear THERMOMETERS

20. Thermocouple This makes use of the thermoelectric effect Thermoelectric device - A thermoelectric device creates a voltage when there is a different temperature on each side When the junctions of two different conductors, such as copper and constantan wire are at different temperatures, an emf (voltage ) is developed. The relation between emf and temperature difference is not linear. The emf generated is small – typically about 5 mV for a temperature difference of 100 C Advantages Can be used to measure rapidly changing temperatures. Can be used to measure temp of small object THERMOMETERS

21. Thermocouple graph

22. SPECIFIC HEAT CAPACITY When heat energy flows into a substance, its temperature will increase The specific heat capacity is the heat energy (in J) needed to raise the temperature of 1 kg of the substance by 1 K   Heat energy in J Temperature change in K Mass in kg Specific heat capacity in J/K/kg

23. SPECIFIC HEAT CAPACITY

24. LATENT HEAT This is the energy required to change the state of a substance. e.g. melting or boiling.

25. LATENT HEAT Latent Heat of Fusion solid => liquid If you have a glass of a cool drink, well supplied with ice, you can expect its temperature to drop until it is close to 0ºC. You also can expect (and can easily check with a thermometer) that it will remain cold, regardless of the outside temperature, as long as there remains some unmelted ice in the drink. Only after all the ice has melted will the temperature of the drink begin to rise .

26. LATENT HEAT Latent Heat of Vaporization liquid => solid

27. LATENT HEAT Why do things expand when they get hotter?

28. SPECIFIC LATENT HEAT The specific latent heat, l of a substance is the energy required to change the state of unit mass of the substance without change of temperature

29. SPECIFIC LATENT HEAT Phase Changes