# Heat a form of Energy By Neil Bronks.

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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).

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

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

Show them the CVGT

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

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

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

Temperature in Celsius
43 23 Length in cm

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

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

Calibration Movie

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.

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

Thermometer Challenge?

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

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.

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

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

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 1m2 where the temperature difference is 1k Q/t (θ+1)0C θ0C 1m2

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 System

Sea Breezes Day – On Shore HOT LAND WARM SEA

Sea Breeze Night Night – Off Shore COLD LAND WARM SEA

Radiation 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.

Solar Constant 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/W LC Ord 2006 Q 7 LC Ord 2004 Q7

Heating a solid Temperature Boiling point Melting point Time

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

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

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

Heat Capacity Amount of heat to raise temperature of this tank by 1 degree Celsius Specific Heat Capacity-Amount of heat to raise temperature of 1kg by 1oC

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

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

(Where c=390 j/kg/kelvin)
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

(Where c=4200 j/kg/kelvin)
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 = Joules

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

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

(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)

Classwork LC Ord Q 7

Heat that changes state without changing temperature
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.

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

A lot more than heating it up!
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!

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

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

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

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

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

2011 Question 7 (a) [Higher Level]
When making a hot drink, steam at 100 °C is added to 160 g of milk at 20 °C. If the final temperature of the drink is to be 70 °C, what mass of steam should be added? You may ignore energy losses to the surroundings. A metal spoon, with an initial temperature of 20 °C, is then placed in the hot drink, causing the temperature of the hot drink to drop to 68 °C. What is the heat capacity of the spoon? You may ignore other possible heat transfers. (cmilk = 3.90 × 103 J kg–1 K–1, cwater = 4.18 × 103 J kg–1 K–1, chot drink = 4.05 × 103 J kg–1 K–1 specific latent heat of vaporisation of water = 2.34 × 106 J kg–1)

H/W Higher level 2005 Q2

Temperature of a kilogram of ice and a kilogram of boiling water?
A kilogram of ice at 0oC and a kilogram (liter) of boiling water at 100oC are mixed together in a thermally insulated tank. What is the temperature of the water in the tank after the contents have reached equilibrium?

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

Energy supplied electrically = Energy gained by metal block
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
12 V a.c. Power supply 10°C Joule meter Digital thermometer Cover 350 J Water Lagging Calorimeter Heating coil

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.

Electrical energy supplied = energy gained by (water +calorimeter)
Q = mwcw mcalccal. Precautions 1/. Lagging 2/. Cool water slightly so final temperature not far from room temperature.

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

1. Place some copper rivets in a boiling tube
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 lagging 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.

7. Stir the water and record the highest temperature θ2.
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 cco2 = mw cw1 + mc cc1

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

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 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 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
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)

In an experiment to measure the specific latent heat of fusion of ice, warm water was placed in a copper calorimeter. Dried, melting ice was added to the warm water and the following data was recorded. Mass of calorimeter 60.5 g Mass of calorimeter + water g Temperature of warm water 30.5 oC Mass of ice 15.1 g Temperature of water after adding ice 10.2 oC Explain why warm water was used. Why was dried ice used? Why was melting ice used? Describe how the mass of the ice was found. What should be the approximate room temperature to minimise experimental error? Calculate the energy lost by the calorimeter and the warm water. Calculate the specific latent heat of fusion of ice.

The balancing energy losses before and after the experiment.
To remove melted ice would have already gained latent heat Melting ice is at 0 oC. Final mass of calorimeter + contents minus mass of calorimeter + water. 20 0C / midway between initial and final temperatures (of the water in the calorimeter) {energy lost = } (mcΔθ )cal + (mcΔθ )warm water = (0.0605)(390)(20.3) + (0.0583)(4200)(20.3) = / J {Energy gained by ice and by melted ice =} (ml)ice + (mcΔθ )melted ice / (0.0151)l + (0.0151)(4200)(10.2) / l (equate:) l = l = × 105 ≈ 3.2 × 105 J kg–1

H/W LC Higher 2003 Q 2

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

1.      Set up as shown 2.    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 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/W LC Ord 2003 Q 2

Lets do the h/w folks LC Ord 2007 Q 3 LC Ord 2005 Q 12(a)
Higher Q 2 LC Higher Q 2 LC Ord Q 2