Ch 12&13 Heat And Temperature


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Ch 12&13 Heat And Temperature

  1. 1. Chapter12: Temperature and Heat
  2. 2. COMMON TEMPERATURE SCALES Celsius to Fahrenheit C l i t F h h it T (F) = [1.8 x T (C)] + 32 Fahrenheit to Celcius T (C) = T (F) – 32 / 1 8 1.8 Celsius to Kelvin Kelvin, Kelvin to Celsius T (C) = T (K) – 273 T (K) = T (C) + 273
  3. 3. LINEAR THERMAL EXPANSION OF A SOLID • The increase in any one dimension of a solid iis called li f lid ll d linear expansion. i • The change in length is directly proportional to the change in temperature : ∆L ≈ ∆T • The length of an object changes when its temperature changes: p g ΔL = α Lo ΔT • Common Unit for the Coefficient of Linear Expansion: 1 = (Co ) −1 Co
  5. 5. VOLUME THERMAL EXPANSION • Th volume of an object changes The l f bj t h when its temperature changes: ΔV = β Vo ΔT coefficient of volume expansion • Common Unit for the Coefficient of Volume Expansion: 1 () o −1 =C o C
  7. 7. HEAT AND INTERNAL ENERGY • Heat is energy that flows from a higher- temperature object to a lower- temperature object p j because of a difference in temperatures. • SI Unit of Heat: joule ( ) j (J) • The heat that flows from hot to cold originates in the internal energy of the hot substance.
  8. 8. Heat and Temperature Change: Specific Heat Capacity •SSpecific H t C ifi Heat Capacity: iis th h t th t must be supplied or it the heat that tb li d removed to change the temperature of a substance. • The amount of heat needed to cause a temperature change p g depends on the mass of the object, size of the temperature change, and the substance of which an object is made Q = mc Δ T • Common Unit for Specific Heat Capacity: J/(kg·Co) p p y /( g
  9. 9. Example: A Hot Jogger In a half-hour, a 65-kg jogger can generate 8.0x105J of heat. This heat is removed from the body by a variety of means, including the b d ’ th body’s own temperature-regulating mechanisms. If the heat t t l ti hi th h t were not removed, how much would the body temperature increase? Q = mcΔT 8.0 × 105 J Q ΔT = = = 3. 5 C o [ )] ( mc (65 kg ) 3500 J kg ⋅ Co
  10. 10. Sample problem • How much heat is needed to increase the temperature of 200 g of water p 5.0°C? (cwater1.0 kcal/(kg.C°) • How much heat is needed to increase the temperature of 200 g of lead 5.0 C? 5.0°C? (c lead = 0.030cal/g °C) C)
  11. 11. Heat Units other than Joule • Kilocalorie – The amount of heat needed to raise the temperature of 1kg of water by one Celcius degree Q = mcΔT – c = 1.0 kcal/(kg.C°) • B iti h Thermal Unit (Btu) British Th l U it (Bt ) – Amount of heat needed to raise the temperature of one pound of water by one Fahrenheit degree. • Joule – There is a relationship between energy in work and energy in heat. – 1kcal = 4186 joules or 1 cal = 4.186 joules – Also known as mechanical equivalent of heat
  12. 12. HEAT AND PHASE CHANGE : LATENT HEAT • Phase changes require large amounts of energy compared to the energy needed for temperature changes. • Energy used to cause a phase change does not cause a temperature change change. • The amount of energy g required is proportional to the number of molecules in the object and to the forces acting b t ti between molecules. l l
  13. 13. CONCEPTUAL EXAMPLE • Suppose you are cooking spaghetti and the instructions say “boil p pasta in water for 10 minutes.” To cook spaghetti in an open pot with pg p p the least amount of energy, should you turn up the burner to its fullest so the water vigorously boils, or should you turn down the burner so the water barely boils?
  14. 14. LATENT HEAT • Latent Heat: is the heat supplied or removed in changing the pp gg phase of a mass (m) of a substance Q = mL • SI Units of Latent Heat: J/kg • Latent heat of fusion (Lf): change between solid and liquid phases • Latent heat of vaporization (Lv) change between li id and t th t f i ti ( ): h bt liquid d gas phases • Latent heat o sub a o ( s): change between solid a d gas ae ea of sublimation (L c a ge be ee so d and phases
  15. 15. Chapter 13 The Transfer of Heat
  16. 16. CONVECTION Convection is the process in which heat is carried from one place to another by the bulk movement of a fluid.
  17. 17. CONDUCTION • Conduction is the process whereby h t is transferred h b heat i t f d directly through a material, with any bulk motion of the material playing no role in the transfer. • Movement of heat by atomic collisions; transfer of heat through stationary matter by physical contact hil tt • Materials that conduct heat well are called thermal conductors, and those that conduct heat poorly are called thermal insulators.
  18. 18. The amount of heat Q that is conducted through the bar depends on a number of factors: 1. The time during which conduction takes place. 2. The temperature difference between the ends of the bar. 3. 3 The Th cross sectional area of the bar. ti l f th b 4. The length of the bar.
  19. 19. RADIATION • R di ti Radiation i th process iin which is the hi h energy is transferred by means of electromagnetic waves. • A material that is a good absorber is also a good emitter emitter. • A material that absorbs completely p y is called a perfect blackbody.
  20. 20. DIAGNOSTIC AND THERAPEUTIC USES OF HEAT • Thermography: indication of blood supply g py pp y – Decreased: deficiency in blood flow to a specific region (clotting, stroke) – Increased: malignant tumor g • Heat pads: relaxation of muscles and increased blood flow • Infrared radiation: premature or newborn babies • Microwave or radio diathermy (controlled to affect only intended area) • Ultrasound diathermy (energy carried by the sound can be converted as thermal energy) • Therapeutic Uses of Cold: lowered temperatures as local anesthetic – Ice packs – Cryosurgery (treatment of warts, tumors, Parkinson’s) g ( )
  21. 21. CLINICAL APPLICATION: THERMOMETERS • A thermometer is used in health care to measure and monitor body temperature. temperature • It allows a caregiver to record a baseline temperature when a patient is admitted admitted. • Repeated measurements of temperature are useful to detect deviations from normal levels and also useful in monitoring the effectiveness of current medications or other treatments. • Thermometers are usually made of a thin glass tube containing a liquid. • The temperature is measured by observing how far up the tube the liquid rises. Different liquids have different nonlinear expansions.
  22. 22. TYPES OF CLINICAL THERMOMETERS - DIRECT • EXPANSION : Liquid-in-glass q g LIQUID thermometers are devices consisting of a bulb attached to Clear glass chamber filled with liquid; glass columns are marked with a measurement scale. • PRINCIPLE: Liquid-in-glass Lens front thermometers rely on the principle that a liquid changes its volume relative to its temperature. White backing Capillary
  23. 23. TYPES OF LIQUID EXPANSION THERMOMETERS Q • Mercury in-glass: a thermometer consisting of mercury in a glass tube. • Calibrated marks on the tube allow the temperature to be read by the length of the mercury within the tube, which varies according to the temperature. • ADVANTAGES – Mercury has large and uniform expansion abilities, its silvery appearance allows for easy reading, & stability. • DISADVANTAGES – When liquid mercury is spilled, it forms droplets that accumulate in the tiniest of spaces and emit vapors into the air. It is odorless, colorless, and very t i d toxic. – Occur by breathing vapors, by direct skin contact or by eating food or drinking water contaminated with mercury mercury.
  24. 24. TYPES OF LIQUID EXPANSION THERMOMETERS Q • ALCOHOL-IN-GLASS: Similar to mercury-in- glass thermometer but contains colored alcohol. • ADVANTAGE: less toxic than a mercurial thermometer • DISADVANTAGES: Alcohol has a smaller density of 0.79 g/cm3 [compared to the density densit of mercury = 13.6 g/cm3] With merc r 13 6 ]. alcohol, there is greater increase in volume, requiring either a longer stem or a wider capillary tube.
  25. 25. TYPES OF CLINICAL THERMOMETERS • CHEMICAL - DOT MATRIX OR PHASE CHANGE: Plastic strips or adhesive patches that indicate a temperature in response to the thermal change in chemical dots. • These devices vary in usefulness depending on y p g their resolution. • DOT MATRIX: Each dot contains a different combination of a chemical mixture that will melt and change color from beige to bright blue at a specific temperature. • Temperature readings are indicated by the T t di i di t d b th number on the thermometer that corresponds with the last blue dot. • The device registers a temperature within 60 seconds and can be read after waiting an additional 10 seconds for a stable measurement; the last dot to turn blue constitutes the body temperature.
  26. 26. TYPES OF CLINICAL THERMOMETERS - DIRECT • LIQUID CRYSTAL DISPLAY: A chemical thermometer made by impregnating spots of liquid crystal material onto a spatula spatula. • If mixed with suitable dyes the y transition from solid to liquid phase is demonstrated by the color of the spot. • Liquid crystal paints are also available which can be used to demonstrate temperature distribution by color over parts of the body.
  27. 27. TYPES OF CLINICAL THERMOMETERS - INDIRECT • THERMOCOUPLE: A thermocouple consists of two junctions at two different metals. If the two junctions are at different Thermocouple temperatures, a voltage is p p g produced that depends on the temperature difference • DIGITAL : Electronic digital thermometers are well-known and widely used. They have several advantages including fast response time, ease of reading and the lack of mercury or other potentially harmful liquids q • PACIFIER • ORAL, RECTAL, AXILLARY
  28. 28. TYPES OF CLINICAL THERMOMETERS - INDIRECT • INFRARED: Infrared thermometers measure temperature using electromagnetic radiation such as infrared emitted f if d itt d from object. By bj t B knowing the amount of infrared energy emitted by the object and its emissivity • Tympanic • Temporal Tympanic