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Heat a form of Energy

Heat a form of Energy. By Neil Bronks. Temperature. Measure of how hot or cold something is This is the science version of shouting at a waiter in Ibiza (it really does not help but it’s the best we have). Fixed Point Usually the boiling point and melting points of water.

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Heat a form of Energy

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  1. Heat a form of Energy By Neil Bronks

  2. Temperature • Measure of how hot or cold something is • This is the science version of shouting at a waiter in Ibiza (it really does not help but it’s the best we have).

  3. 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

  4. 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

  5. Show them the CVGT

  6. Emf R Temp Temp Different Temperatures Thermocouple Junction emf Platinum Wire Resistance Because the different thermometric properties react differently at the same temperature

  7. Emf R Pressure Temp Temp Temp Different Thermometers Platinum Wire Resistance CVGT Pressure Thermocouple Junction emf CVG is a standard thermometer and is used to calibrate the others

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

  9. Temperature in Celsius 43 23 Length in cm

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

  11. Kelvin and Celsius • Add 273 to Celsius and you get the temperature in Kelvin • Lowest possible temperature is -273oC • This is zero Kelvin OK

  12. Calibration Movie

  13. 2003 Question 12 (b) [Higher Level] • What is the difference between heat and temperature? • The emf of a thermocouple can be used as a thermometric property.Explain the underlined terms. • Name a thermometric property other than emf. • Explain why it is necessary to have a standard thermometer.

  14. H/W • LC Ord 2007 Q 3 • And LC Ord 2005 Q12(a)

  15. Thermometer Challenge?

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

  17. Conduction In a solid every atom is physically bonded to its neighbours in some way. If heat energy is supplied to one part of a solid, the vibration travels through the solid. Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance.

  18. Practical Conduction • A spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids • It is also why stone and metals appear cold. They are just good conductors. Chilly

  19. Test Tube of water Metal Gauze ICE HEAT Water as a Poor Conductor The ice does not melt as the water is a terrible conductor and convection only works up.

  20. U-Value Q/t • U- Value (or Heat transmittance) 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 (θ+1)0C θ0C 1m2

  21. Convection Most houses have radiators to heat their rooms. This is a bad name for them - as they give off heat mainly by convection! The air expands and is less dense so it rises It cools and falls (So hot fluids rise not heat) CONVECTION CURRENT

  22. Domestic Heating System

  23. Sea Breezes Day – On Shore HOT LAND WARM SEA

  24. Sea Breeze Night Night – Off Shore COLD LAND WARM SEA

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

  26. A silver or white body holds heat in so to reduce heat loss we use silver or white. Black bodies radiate more heat so we paint things black when we want to lose heat.

  27. Vacuum Flask

  28. 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

  29. H/W • LC Ord 2006 Q 7 • LC Ord 2004 Q7

  30. Melting point Boiling point Heating a solid Temperature Time

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

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

  33. Storage Heater • Uses cheap night time electricity to heat up bricks with large heat capacity • Release slowly during the day

  34. Heat Capacity • Amount of heat to raise temperature of this tank by 1 degree Celsius • SpecificHeat Capacity-Amount of heat to raise temperature of 1kg by 1oC

  35. Heat Capacity • Amount of heat to raise temperature of this kettle by 1 degree Celsius (Different from the tank) • SpecificHeat Capacity-Amount of heat to raise temperature of 1kg by 1oC(Same as always)

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

  37. Example How much energy does it take to heat up 2kg of copper by 30 degrees? (Where c=390 j/kg/kelvin) As Q=mc∆ Q= 2 x 390 x 30 = 23400 Joules

  38. Example How much energy does it take to heat up 500ml of water from 20oC to B.P.? (Where c=4200 j/kg/kelvin) As Q=mc∆ Q= 0.5 x 4200 x 80 = 168000 Joules

  39. Class Challenge • Water falls over a waterfall in perfect conditions (surrounded by spherical chickens in a vacuum) at the bottom it is 1 degree hotter than the top. How high is the waterfall? • Take g=9.8 m/s2 and c=4200 j/kg/k

  40. Power • If this takes 5 mins how much power is needed? Power = Work done/ Time = 168000/300s = 560 Watts

  41. 2011 8 (b)[Ordinary Level] • An electric kettle is filled with 500 g of water and is initially at a temperature of 15 0C. • The kettle has a power rating of 2 kW. • Calculate the energy required to raise the temperature of the water to 100 0C. • How much energy is supplied by the kettle every second? • How long will it take the kettle to heat the water to 100 0C? • Name a suitable material for the handle of the kettle. Justify your answer. • (specific heat capacity of water = 4180 J Kg−1 K−1)

  42. Classwork • LC Ord 2008 Q 7

  43. 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.

  44. Latent Heat • Heat-Amount of heat to change state of water in kettle without changing temperature • Specific Latent Heat-Amount of heat to change state of 1kg of water without changing temperature

  45. Example How much energy does it take to turn 2kg of copper into a liquid? (latent heat of fusion of Copper l=38900000 j/kg) As Q=ml Q= 2 x 38900000 = 77800000 Joules A lot more than heating it up!

  46. Frozen Wine A litre of wine at 20 0C. is left in the freezer by accident. It freezes and reduces to -10 0C. How much energy does this take? 3 stages • Cools to zero • Freezes • Cools to -10 0C.

  47. Stage 1 Wine has c=4000j/kg/kelvin, =1kg/litre Using Q=mc =  V c  =1x1x4000x20 =80000joules

  48. Stage 2 Wine has latent heat of fussion l = 300000j/kg Using Q=ml =  V l =1x1x300000 =300000joules

  49. Stage 3 Frozen Wine has c=3000j/kg/kelvin, =1kg/litre Using Q=mc =  V c  =1x1x3000x10 =30000joules Different from liquid

  50. Total = 80000+300000+30000 =410000 joules How long will this take in a 100Watt fridge? 100w = 100 joules/second Time = 410000/100 = 4100 seconds = 4100/3600 = 1.13 hours

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