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Heat

Heat. By Neil Bronks. Fixed Point Usually the boiling point and melting points of water. ------------------------------. Thermometric Property Something that varies Measurably with temperature. Scale Divisions between the fixed points. Thermometers.

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Heat

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  1. Heat By Neil Bronks

  2. Fixed Point Usually the boiling point and melting points of water ------------------------------ Thermometric Property Something that varies Measurably with temperature Scale Divisions between the fixed points Thermometers Three things that make up a thermometer

  3. Emf R Pressure Temp Temp Temp Different Thermometers Platinum Wire Resistance CVGT Pressure Thermocouple Junction emf The only linear thermometric property is the CVG. All the others must be calibrated to the CVG

  4. CALIBRATION CURVE OF A THERMOMETER USING THE LABORATORY MERCURY THERMOMETER AS A STANDARD Alcohol thermometer uncalibrated Mercury thermometer Boiling tube Water Glycerol Heat source

  5. Temperature in Celsius 43 23 Length in cm

  6. Fixed Points – Alternative to Calibration Graph • Use BP and MP of water • Divide up gap between into 100 division scale

  7. Heat Transfer Convection • Hot air rising carrying the heat up with it. Conduction -Transfer by vibrations Radiation -Transfer by Electro-magnetic wave

  8. U-Value • U- Value is a measure of how good an insulator something is. A good insulator has a low U-value. • Defined as the rate of heat energy transfer through 1m2 where the temperature difference is 1k

  9. Radiation • The transfer of heat in the form of an electro-magnetic wave. • Only form of heat that can travel through a vacuum

  10. Solar Constant • The average amountof solar energy falling on 1 square meter of atmosphere per second • About 1.35kWm-2 At the poles the same amount of energy from the sun is spread over a much larger surface area. Than the equator

  11. Boiling point Heat raises temperature Energy=mcΔθ Boiling Melting point Liquid Melting Latent Heat Only Energy=ml Solid Heating a solid Temperature Gas Time

  12. Liquid boils and takes in Latent Heat from the food Gas turns back into a liquid giving out heat The Refrigerator Liquid Gas Compressor

  13. Heating Up Heat that raises temperature Energy Supplied=mcΔθ Where m = mass of body Δθ=Change in Temperature c = Specific Heat Capacity Amount of heat energy to raise 1kg by 1k

  14. Latent Heat Heat that changes state without changing temperature Energy Supplied=ml Where m = mass of body l = Specific Latent Heat Amount of heat energy to change state of1kg without changing temp.

  15. MEASUREMENT OF SPECIFIC HEAT CAPACITY OF WATER BY AN ELECTRICAL METHOD Joule meter 12 V a.c. Power supply Cover Digital thermometer Water Lagging Calorimeter Heating coil 10°C 350 J

  16. Electrical energy supplied = energy gained by (water +calorimeter) Q = mwcw + mcalccal. Precautions 1/. Lagging 2/. Cool water slightly so final temperature not far from room temperature.

  17. Cotton wool 10°C Boiling tube Water Digital thermometer Copper rivets Water Lagging Calorimeter Heat source MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL OR WATER BY A MECHANICAL METHOD

  18. 6.Quickly add the hot copper rivets to the calorimeter, without splashing. 7.Stir the water and record the highest temperature θ2. 8.Find the mass of the calorimeter plus water plus copper rivets m2 and hence find the mass of the rivets mco. Heat lost by the Rivets=Heat gained by water and calorimeter mco cco = mw cw +mc cc

  19. MEASUREMENT OF THE SPECIFIC LATENT HEAT OF FUSION OF ICE 10°C Wrap ice in cloth to crush and dry. Crushed ice Digital thermometer Calorimeter Water Lagging

  20. CalculationsEnergy gained by ice = Energy lost by calorimeter + energy lost by the water.milf+micw1= mcalcc 2+mwcw 2milf+micw(f-0)= mcalcc (i- f) +mwcw (i- f)

  21. MEASUREMENT OF THE SPECIFIC LATENT HEAT OF VAPORISATION OF WATER Lagging Water Heat source 10°C Digital Thermometer Steam Trap Calorimeter

  22. Energy lost by steam = energy gained by calorimeter + energy gained by the watermsl+msc. ∆ = mcalcc ∆+mwcw.∆mslv+mscw(100-f)= mcalcc (f- I) +mwcw (f- I)

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