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