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Heat a form of Energy By Neil Bronks By Neil Bronks.

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Presentation on theme: "Heat a form of Energy By Neil Bronks By Neil Bronks."— Presentation transcript:

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2 Heat a form of Energy By Neil Bronks By Neil Bronks

3 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 its the best we have). 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 its the best we have).

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

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

6 Show them the CVGT

7 Different Temperatures Thermocouple Junction emf Thermocouple Junction emf Platinum Wire Resistance Because the thermometric properties are non- linear we may get different readings for the same temperature Emf Temp R

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

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

10 Temperature in Celsius Length in cm 23 43

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

12 Kelvin and Celsius Add 273 to Celsius and you get the temperature in Kelvin Lowest possible temperature is -273 o C This is zero Kelvin OK Add 273 to Celsius and you get the temperature in Kelvin Lowest possible temperature is -273 o C This is zero Kelvin OK

13 Calibration Movie

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

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

16 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.

17 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. 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

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

19 U-Value 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 1m 2 where the temperature difference is 1k 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 1m 2 where the temperature difference is 1k θ0Cθ0C Q/t 1m 2 (θ+1) 0 C

20 ConvectionConvection 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

21 Domestic Heating System

22 Sea Breezes HOT LAND WARM SEA Day – On Shore

23 Sea Breeze Night COLD LAND WARM SEA Night – Off Shore

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

25 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.

26 Vacuum Flask

27 Solar Constant The average amount of solar energy falling on 1 square meter of atmosphere per second About 1.35kWm -2 The average amount of 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

28 H/W LC Ord 2006 Q 7 LC Ord 2004 Q7 LC Ord 2006 Q 7 LC Ord 2004 Q7

29 Heating a solid Temperature Time Melting point Boiling point

30 Heating a solid Temperature Time Boiling point Melting point Melting Solid Boiling Liquid Gas Heat raises temperature Energy=mc Δθ Latent Heat Only Energy=ml

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

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

33 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 = Joules 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 = Joules

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

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

36 H/W LC Ord 2008 Q 7 LC Ord 2008 Q 7

37 Latent Heat Heat that changes state without changing temperature Energy Supplied=ml Where m = mass of body l = Specific 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.

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

39 Frozen Wine A litre of wine at 20 0 C. is left in the freezer by accident. It freezes and reduces to C. How much energy does this take? 3 stages 1. Cools to zero 2. Freezes 3. Cools to C. A litre of wine at 20 0 C. is left in the freezer by accident. It freezes and reduces to C. How much energy does this take? 3 stages 1. Cools to zero 2. Freezes 3. Cools to C.

40 Stage 1 Wine has c=4000j/kg/kelvin, =1kg/litre Using Q=mc = V c =1x1x4000x20 =80000joules Wine has c=4000j/kg/kelvin, =1kg/litre Using Q=mc = V c =1x1x4000x20 =80000joules

41 Stage 2 Wine has latent heat of fussion l = j/kg Using Q=ml = V l =1x1x =300000joules Wine has latent heat of fussion l = j/kg Using Q=ml = V l =1x1x =300000joules

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

43 Total = = joules How long will this take in a 100Watt fridge? 100w = 100 joules/second Time = /100 = 4100 seconds = 4100/3600 = 1.13 hours = = joules How long will this take in a 100Watt fridge? 100w = 100 joules/second Time = /100 = 4100 seconds = 4100/3600 = 1.13 hours

44 H/W Higher level 2005 Q2 Higher level 2005 Q2

45 MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL BY AN ELECTRICAL METHOD Heating coil Lagging Metal block 12 V a.c. Power supply Joule meter 350 J 10°C Glycerol

46 1. Find the mass of the metal block m. 2. Set up the apparatus as shown in the diagram. 3. Record the initial temperature θ 1 of the metal block. 4. Zero the joule meter and allow current to flow until there is a temperature rise of 10 C. 6. Switch off the power supply, allow time for the heat energy to spread throughout the metal block and record the highest temperature θ Record the final joule meter reading Q. Energy supplied electrically = Energy gained by metal block Q = mc ( θ 2 – θ 1 )

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

48 1. Find the mass of the calorimeter m cal. 2. Find the mass of the calorimeter plus the water m 1. Hence the mass of the water m w is m 1 – m cal. 3. Set up the apparatus as shown. Record the initial temperature θ Plug in the joule meter, switch it on and zero it. 5. Switch on the power supply and allow current to flow until a temperature rise of 10 C has been achieved. 6. Switch off the power supply, stir the water well and record the highest temperature θ 2. Hence the rise in temperature is θ 2 – θ Record the final joule meter reading Q.

49 Precautions 1/. Lagging 2/. Cool water slightly so final temperature not far from room temperature. Electrical energy supplied = energy gained by (water +calorimeter) Q = m w c w + m cal c cal.

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

51 1. Place some copper rivets in a boiling tube. Fill a beaker with water and place the boiling tube in it. 2. Heat the beaker until the water boils. Allow boiling for a further five minutes to ensure that the copper pieces are 100° C. 3. Find the mass of the copper calorimeter m cal. 4. Fill the calorimeter, one quarter full with cold water. Find the combined mass of the calorimeter and water m Record the initial temperature of the calorimeter plus water θ 1. Place in lagging 6. Quickly add the hot copper rivets to the calorimeter, without splashing. 7. Stir the water and record the highest temperature θ Find the mass of the calorimeter plus water plus copper rivets m 2 and hence find the mass of the rivets m co.

52 6. Quickly add the hot copper rivets to the calorimeter, without splashing. 7. Stir the water and record the highest temperature θ Find the mass of the calorimeter plus water plus copper rivets m 2 and hence find the mass of the rivets m co. Heat lost by the Rivets=Heat gained by water and calorimeter m co c co 2 = m w c w 1 + m c c c 1

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

54 1. Place some ice cubes in a beaker of water and keep until the ice-water mixture reaches 0 °C. 2. Find the mass of the calorimeter m cal. Surround with lagging 3. Half fill the calorimeter with water warmed to approximately 10 °C above room temperature. Find the combined mass of the calorimeter and water m Record the initial temperature θ 1 of the calorimeter plus water. 5. Surround the ice cubes with kitchen paper or a cloth and crush them between wooden blocks – dry them with the kitchen paper. 6. Add the pieces of dry crushed ice, a little at a time, to the calorimeter. 7. Record the lowest temperature θ 2 of the calorimeter. Find the mass of the calorimeter + water + melted ice m 3

55 Calculations Energy gained by ice = Energy lost by calorimeter + energy lost by the water. m i l f +m i c w 1 = m cal c c 2 +m w c w 2 m i l f +m i c w ( f -0)= m cal c c ( i - f ) + m w c w ( i - f )

56 H/W LC Higher 2003 Q 2 LC Higher 2003 Q 2

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

58 1. Set up as shown 2. Find the mass of the calorimeter m cal. 3. Half fill the calorimeter with water cooled to approximately 10 °C below room temperature. 4. Find the mass m 1 of the water plus calorimeter. 5. Record the temperature of the calorimeter + water θ Allow dry steam to pass into the water in the calorimeter until temperature has risen by about 20 °C. 7. Remove the steam delivery tube from the water, taking care not to remove any water from the calorimeter in the process. 8. Record the final temperature θ 2 of the calorimeter plus water plus condensed steam. 9. Find the mass of the calorimeter plus water plus condensed steam m 2.

59 Energy lost by steam = energy gained by calorimeter + energy gained by the water m s l+m s c. = m cal c c +m w c w. m s l v +m s c w (100- f )= m cal c c ( f - I ) + m w c w ( f - I )

60 H/W LC Ord 2003 Q 2 LC Ord 2003 Q 2

61 Lets do the h/w folks LC Ord 2007 Q 3 LC Ord 2005 Q 12(a) LC Ord 2006 Q 7 LC Ord 2004 Q 7 LC Ord 2008 Q 7 Higher 2005 Q 2 LC Higher 2003 Q 2 LC Ord 2003Q 2 LC Ord 2007 Q 3 LC Ord 2005 Q 12(a) LC Ord 2006 Q 7 LC Ord 2004 Q 7 LC Ord 2008 Q 7 Higher 2005 Q 2 LC Higher 2003 Q 2 LC Ord 2003Q 2


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