Presentation on theme: "Heat and Temperature Heat is a form of energy, and is measured in Joules (J). Temperature is different from heat. Temperature is a measure of how hot or."— Presentation transcript:
1 Heat and TemperatureHeat is a form of energy, and is measured in Joules (J).Temperature is different from heat.Temperature is a measure of how hot or cold an object is.It is measured in degrees Celsius (°C).Heat can move from one place to another.The three methods of heat travel are:conductionconvectionradiation
8 Air heats up and rises over land, cools down and falls over sea. Day BreakLand is warmer than sea.Air heats up and rises over land, cools down and falls over sea.SunsetSea is warmer than land.Air cools and falls over land, but is warmed over the sea and rises.
10 RadiationExperimentA metallic cube known as a “Leslie Cube” is filled with boiling water.
11 All hot objects radiate heat energy. Radiated heat waves are also known as INFRARED RADIATION.It travels at the speed of light (3 x 108 ms-1).Matt black surfaces radiate more heat than shiny surfaces at the same temperature.Infrared radiation can travel through a vacuum (just as heat from sun is able to travel through space which is a vacuum).
12 Black fur poses no disadvantage as only active at night Lemur Nocturnal LemurBlack fur poses no disadvantage as only active at nightLemurActive during the day so has lighter fur.On cold mornings points its belly to the sun.
14 Preventative Action Heat Lost Type Reducing Heat LossPreventative ActionHeat Lost Typecavity wall insulationconductiondouble glazingconductioncarpetsconductionloft insulationconvectiondraft excludersconvectionshiny foil behind radiatorsradiationHeat energy is lost faster when there is a difference in temperature between inside and outside.bigger
15 Heat EnergyThe amount of heat energy required to heat up an object depends on:the mass of the substance ( m )the material the object is made ofthe rise in temperature required ( ΔT )The amount of heat energy is given by:
16 x÷EHcmΔTQuantityUnitHeat Energy ( EH )Specific Heat Capacity ( c )Mass ( m )Change in Temperature ( ΔT )Joules ( J )Joules per kilogram per degrees Celsius ( J kg-1 °C-1 )Kilograms ( kg )Degrees Celsius ( °C )** Specific Heat Capacities can be found on Data Sheet in exam paper **Specific Heat Capacity is the amount of energy required to raise the temperature of 1 kg of a substance by 1 °C.
17 Example 1Calculate the amount of heat energy required to raise the temperature of 2 kg of water from 20 °C to 100 °C.** data sheet **
18 A 3 kg block of copper at 15 °C is heated. Example 2A 3 kg block of copper at 15 °C is heated.Calculate the rise in temperature if 20 kJ of heat energy is transferred to the copper.** data sheet **
19 Example 30.5 kg of a liquid is heated from 8 °C to 40 °C by 50 kJ of heat energy.Calculate the specific heat capacity of the liquid.
20 Yellow BookHeat Energy – Page 90Q79 (a) (b) (c) and (d)Q80, Q81, Q82, Q83, Q84, Q85
21 Power of a Heater Experiment Joulemeter 12 volt Immersion Heater to 12 V a.c. supplystopwatch
22 Zero the joulemeter.Switch on for 20 seconds and record the energy used.
23 Specific Heat Capacity ExperimentThe specific heat capacity of aluminium is measured using the apparatus shown.to 12 V a.c. supplythermometerheateraluminium blockstopwatch
24 Initial temperature of block °C. The heater is switched on for 5 minutes.Final temperature of block °C.Heat Energy Used
25 Specific Heat Capacity The value measured experimentally is higher than 380 J kg-1 °C-1.This is because not all the heat energy is transferred to the aluminium block – some is lost to the surroundings.
26 Combining EH = cmΔT and E = Pxt The heat energy equation is:The equation for electrical power is:Since E = P x t we can write P x t instead of E.** NOT on data sheet **
27 Example 12 kg of water is heated from 20°C to 60°C by a 2 kW heater.Calculate the time taken.
28 QuestionsQ kg of copper is heated from 15 °C to 50 °C by a 60 W heater.Calculate the time taken.Q2. 2 kg of water at 10 °C is heated by a 1.5 kW heater for 3 mins.Calculate the final temperature of the water.Q3. How long will it take a 2.3 kW heater to boil 0.5 kg of water with an initial temperature of 10 °C.112.6 sΔT = 32.3 °C so Tfin = 42.3 °C81.8 s
29 Measuring & Calculating Time Taken ExperimentThe time taken for a kettle to boil is measured and calculated.The measured time taken for the kettle to boil is s.
30 Variations of EH = cmΔT There are several formulae for energy. These can be used to do heat calculations.** NOT on data sheet **
31 Example 1A heater operates from the 230 V mains supply and takes a current of 3 A.This heater is used to heat up 2 kg of water at 18 °C.The heater is switched on for 5 minutes.Calculate the rise in temperature of the water and then state the final temperature reached.
33 All the kinetic energy is transferred into heat energy (EK = EH) Example 2A lead bullet of mass 0.05 kg has a speed of 80 ms-1.The bullet hits a wall and stops.Calculate the rise in temperature of the bullet as it does this.(clead = 130 J kg-1 °C-1)All the kinetic energy is transferred into heat energy (EK = EH)
34 QuestionA 2.2 kW kettle contains 1.7 kg of water at 12 °C.The kettle is switched on for 4 minutes.(a) Calculate the maximum temperature reached by the water.(b) In practice, will the maximum temperature reached be bigger or smaller than this calculated value.Explain your answer fully.
39 A graph of the temperature against time is plotted for the cooling salol. change of statetemperature(°C)BC38DEtimeDuring a change of state – NO CHANGE IN TEMPERATURE.
40 liquid salol turns to a solid (solidifies) StageDescriptionABliquid cools downBCliquid salol turns to a solid (solidifies)latent (hidden) heat is given outtemperature stays the sameCDsolid salol cools down to room temp.DEsalol is at room temp. so no further fall in temperatureABCDEtemperature(°C)time38
41 Change of State Solid Liquid Gas The changes of state are: melting evaporationSolidLiquidGasfreezingcondensation
42 Latent Heat of Fusion (melting) The amount of heat energy required to melt a solid depends on:the mass of the solidwhat substance the solid is made of.This gives the equation:
43 x÷EHmLfQuantityUnitHeat Energy ( EH )Mass ( m )Specific Latent Heat of Fusion ( Lf )Joules ( J )Kilograms ( kg )Joules per Kilogram ( J kg-1 )Specific Latent Heat of Fusion is the amount of energy required to change 1 kg of a substance from solid to liquidThe specific latent heat of fusion for water is 3.34 x 105 J kg-1.
44 Example 1Calculate the energy required to melt 2 kg of ice at 0 °C.
45 Example 2Calculate the time taken by a 500 W heater to completely melt 2 kg of ice at 0 °C.
46 Questions1. Calculate the heat energy required to melt 2.7 kg of ice at 0 °C.2. A 700 W heater inside a block of ice at 0 °C is switched on for 3 minutes.Calculate the mass of ice which will melt.3. A 1 kW heater inside a block of ice at 0 °C is switched on.The heater melts 0.65 kg of ice.Calculate the time that the heater was switched on for.
47 Measuring Specific Latent Heat of Fusion of Ice ExperimentJoulemeterIce at 0 °CHeater(not switched on)WaterBeaker 1Beaker 2Control Experiment
48 The control experiment is not switched on. The control measures the amount of ice that melts due to temperature of the room.The heater connected to the joulemeter is switched on for 5-minutes.The amount of ice melted in beaker 2 is subtracted from the amount melted in beaker 1.Results
49 The data booklet value is 3.34 x 105 J kg-1. Q. Why is the measured value less than the data book vale?The measured value is less than 3.34 x 105 J kg-1 as heat energy is lost to the surroundings.
50 Latent Heat of Vaporisation The heat energy needed to boil away a liquid (vaporise) depends on:the mass of liquidwhat the liquid is.This gives the equation:The specific latent heat of vaporisation of water is 2.26 x 106 J kg-1.
51 Questions1. Calculate the energy required to turn 3kg of water at 100 °C into steam at 100 °C.2. Calculate the time taken by a 2 kW kettle to boil away 0.5 kg of water at 100 °C.
52 Measuring Specific Latent Heat of Vaporisation ExperimentThe mass of the kettle and water is measured.The kettle is kept on for 5 minutes while the water boils.The new mass of the kettle and boiling water is taken.water1,850 W heating element
54 Applications Involving a Change of State Cool Boxfrozen packA frozen pack is placed inside the cool box.It absorbs heat energy from the air and the food inside.The frozen pack melts ( solid to liquid ).The air and food are cooler.
55 The Fridgethe motor pumps a liquid through pipe work inside fridge.the liquid absorbs (latent) heat energy, and changes to a gas.air inside fridge becomes cooler.compressor changes gas back to a liquid.gas loses heat energy as travels through pipes at rear.McompressorHeatHeat
56 Complex Heat Calculations Example 1(a) Calculate the heat energy required to turn 0.5 kg of ice at 0°C into water at 20°C.cwater = 4180 J kg-1 °C-1 Lf ice = 3.34 x 105 J kg-1There are 2 parts to this problem:melting iceheating water
58 (b) How long would it take a 700 W kettle to do this? x÷EPt
59 (b) Calculate the time it would take a 600 W heater to do this. Questions(a) Calculate the heat energy required to turn 1.2 kg of ice at 0°C into water at 18°C.(b) Calculate the time it would take a 600 W heater to do this.400, ,288 = 491,088 J818.5 seconds
60 A 0.2 kg mass of a solid substance is heated by a 150 W heater. A graph of temperature against time for the substance as it is heated is shown.time (s)temperature (°C)104050250(a) What happens between 50 and 250 seconds?(b) What is the melting point (temperature) of the solid?(c) Calculate the specific heat capacity of the solid.(d) Calculate the specific latent heat of fusion of the substance.change of state40 °C1250 J kg-1 °C-1150,000 J kg-1`