heat a form of energy by neil bronks by neil bronks
TRANSCRIPT
Heat a form of EnergyHeat a form of Energy
ByNeil Bronks
ByNeil Bronks
TemperatureTemperature
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).
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).
ThermometersThermometersThree things that make up a thermometer
Thermometric PropertySomething that varies
Measurably with temperature
Fixed PointUsually the
boiling point and melting points
of water
ScaleDivisions between
the fixed points
------------------------------
Different ThermometersDifferent ThermometersThermocoupleJunction emfThermocoupleJunction emf
Platinum Wire
Resistance
CVGTPressure
The only linear thermometric property is the CVG. All the others must be calibrated to the CVG
Emf
Temp
Pressure
Temp
R
Temp
Show them the CVGTShow them the CVGT
Different TemperaturesDifferent TemperaturesThermocoupleJunction emfThermocoupleJunction emf
Platinum Wire
Resistance
Because the thermometric properties are non-linear we may get different readings for the same temperature
Emf
Temp
R
Temp
Different ThermometersDifferent ThermometersThermocoupleJunction emfThermocoupleJunction emf
Platinum Wire
Resistance
CVGTPressure
CVG is a standard thermometer and is used to calibrate the others
Emf
Temp
Pressure
Temp
R
Temp
CALIBRATION CURVE OF A THERMOMETER USING THE LABORATORY MERCURY THERMOMETER AS A
STANDARD
CALIBRATION CURVE OF A THERMOMETER USING THE LABORATORY MERCURY THERMOMETER AS A
STANDARD
Heat source
Mercury thermometer
Boiling tube
Glycerol Water
Alcohol thermometer uncalibrated
Temperature in Celsius
Length in cm23
43
Fixed Points – Alternative to Calibration Graph
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
Kelvin and CelsiusKelvin and Celsius
Add 273 to Celsius and you get the temperature in Kelvin
Lowest possible temperature is -273oC
This is zero Kelvin OK
Add 273 to Celsius and you get the temperature in Kelvin
Lowest possible temperature is -273oC
This is zero Kelvin OK
Calibration MovieCalibration Movie
H/WH/W
LC Ord 2007 Q 3
And LC Ord 2005 Q12(a)
LC Ord 2007 Q 3
And LC Ord 2005 Q12(a)
Heat TransferHeat Transfer
Conduction-Transfer
byvibrations
Radiation-Transfer by
Electro-magnetic wave
Convection- Hot air
risingcarrying
theheat up with it.
ConductionConductionIn 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.
Practical ConductionPractical 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
Water as a Poor Conductor
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
U-ValueU-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 1m2 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 1m2 where the temperature difference is 1k
θ0C
Q/t
1m2
(θ+1)0C
ConvectionConvection
Most houses have radiators to heat their rooms. This is a bad name for them - as they give off heat mainly by 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
Domestic Heating SystemDomestic Heating System
Sea BreezesSea Breezes
HOT LAND WARM SEA
Day – On Shore
Sea Breeze NightSea Breeze Night
COLD LAND WARM SEA
Night – Off Shore
RadiationRadiation
The transfer of heat in the form of an electro-magnetic wave.
Only form of heat that can travel through a vacuum
The transfer of heat in the form of an electro-magnetic wave.
Only form of heat that can travel through a vacuum
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.
Vacuum FlaskVacuum Flask
Solar ConstantSolar 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
H/WH/W
LC Ord 2006 Q 7
LC Ord 2004 Q7
LC Ord 2006 Q 7
LC Ord 2004 Q7
Heating a solidHeating a solid
Temperature
Time
Melting point
Boiling point
Heating a solidHeating a solidTemperature
Time
Boiling point
Melting point
Melting
Solid
Boiling
Liquid
GasHeat raises temperatureEnergy=mcΔθ
Latent Heat OnlyEnergy=ml
The RefrigeratorThe Refrigerator
Compressor
Liquid GasLiquid boils and takes in Latent Heat from the food
Gas turns back into a liquid giving out heat
Heating UpHeating Up
Heat that raises temperatureEnergy Supplied=Q=mcΔθ
Where m = mass of bodyΔθ=Change in Temperaturec = Specific Heat Capacity
Heat that raises temperatureEnergy Supplied=Q=mcΔθ
Where m = mass of bodyΔθ=Change in Temperaturec = Specific Heat Capacity
Amount of heat energy to raise
1kg by 1k
ExampleExample
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
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
ExampleExample
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
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
PowerPower
If this takes 5 mins how much power is needed?
Power = Work done/ Time = 168000/300s = 560 Watts
If this takes 5 mins how much power is needed?
Power = Work done/ Time = 168000/300s = 560 Watts
H/WH/W
LC Ord 2008 Q 7
LC Ord 2008 Q 7
Latent HeatLatent Heat
Heat that changes state without changing temperatureEnergy Supplied=ml
Where m = mass of bodyl = Specific Latent Heat
Heat that changes state without changing temperatureEnergy Supplied=ml
Where m = mass of bodyl = Specific Latent Heat
Amount of heat energy to change state of1kg
without changing temp.
ExampleExample
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=mlQ= 2 x 38900000= 77800000 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=38900000 j/kg)
As Q=mlQ= 2 x 38900000= 77800000 Joules
A lot more than heating it up!
Frozen WineFrozen 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 stages1. Cools to zero2. Freezes3. Cools to -10 0C.
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 stages1. Cools to zero2. Freezes3. Cools to -10 0C.
Stage 1Stage 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
Stage 2Stage 2
Wine has latent heat of fussion l = 300000j/kg
Using Q=ml= V l
=1x1x300000=300000joules
Wine has latent heat of fussion l = 300000j/kg
Using Q=ml= V l
=1x1x300000=300000joules
Stage 3Stage 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
TotalTotal= 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
= 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
H/WH/W
Higher level 2005 Q2
Higher level 2005 Q2
MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL BY AN
ELECTRICAL METHOD
MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL BY AN
ELECTRICAL METHOD
Heating coil
LaggingMetal block
12 V a.c. Power supply
Joule meter
350 J
10°C
Glycerol
1. Find the mass of the metal block m.2. Set up the apparatus as shown in the diagram.3. Record the initial temperature θ1 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 θ2.8. Record the final joule meter reading Q.
Energy supplied electrically = Energy gained by metal block
Q = mc (θ2 – θ1)
MEASUREMENT OF SPECIFIC HEAT CAPACITY
OF WATER BY AN ELECTRICAL METHOD 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 Digitalthermometer
10°C
1. Find the mass of the calorimeter mcal.2. Find the mass of the calorimeter plus the water m1. Hence the mass of the water mw is m1 – mcal.3. Set up the apparatus as shown. Record the initial temperature θ1.
4. 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 θ2. Hence the rise in temperature is θ2 – θ1. 7. Record the final joule meter reading Q.
Precautions 1/. Lagging
2/. Cool water slightly so final temperature not far from room temperature.
Electrical energy supplied = energy gained by (water +calorimeter)
Q = mwcw + mcalccal.θ θ
MEASUREMENT OF THE SPECIFIC HEAT CAPACITY OF A METAL OR WATER BY A
MECHANICAL METHOD
10°C
CalorimeterLagging
Cotton wool
Water
Copper rivets
Boiling tube
Heat source
Digitalthermometer
Water
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 mcal.4. Fill the calorimeter, one quarter full with cold water. Find the combined mass of the calorimeter and water m1.5. Record the initial temperature of the calorimeter plus water θ1. Place in lagging6. 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.
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 cco2 = mw cw1 + mc cc1
MEASUREMENT OF THE SPECIFIC LATENT HEAT OF FUSION OF ICE
Wrap ice in cloth to crush and dry.
Calorimeter
Lagging
Crushed ice
Water
Digitalthermometer
10°C
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 mcal. Surround with lagging3. Half fill the calorimeter with water warmed to approximately 10 °C above room temperature. Find the combined mass of the calorimeter and water m2. 4. Record the initial temperature θ1 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 θ2 of the calorimeter.Find the mass of the calorimeter + water + melted ice m3
Calculations
Energy gained by ice = Energy lost by calorimeter + energy lost by the water.
milf +micw 1= mcalcc 2+mwcw 2
milf +micw (f-0)= mcalcc (i- f) +mwcw (i- f)
Calculations
Energy gained by ice = Energy lost by calorimeter + energy lost by the water.
milf +micw 1= mcalcc 2+mwcw 2
milf +micw (f-0)= mcalcc (i- f) +mwcw (i- f)
H/WH/W
LC Higher 2003 Q 2
LC Higher 2003 Q 2
MEASUREMENT OF THE SPECIFIC LATENT HEAT OF VAPORISATION OF
WATER
MEASUREMENT OF THE SPECIFIC LATENT HEAT OF VAPORISATION OF
WATER
Heat source
10°C
Lagging
DigitalThermometer
Water
Steam Trap
Calorimeter
1. Set up as shown2. Find the mass of the calorimeter mcal.3. Half fill the calorimeter with water cooled to approximately 10 °C below room temperature.4. Find the mass m1 of the water plus calorimeter.5. Record the temperature of the calorimeter + water θ1.
6. 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 θ2 of the calorimeter plus water plus condensed steam. 9. Find the mass of the calorimeter plus water plus condensed steam m2.
Energy lost by steam = energy gained by calorimeter + energy gained by the water
msl+msc. ∆ = mcalcc ∆
+mwcw.∆
mslv +mscw (100-f)= mcalcc (f-
I) +mwcw (f- I)
Energy lost by steam = energy gained by calorimeter + energy gained by the water
msl+msc. ∆ = mcalcc ∆
+mwcw.∆
mslv +mscw (100-f)= mcalcc (f-
I) +mwcw (f- I)
H/WH/W
LC Ord 2003 Q 2
LC Ord 2003 Q 2
Lets do the h/w folksLets 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 2003 Q 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 2003 Q 2