Heat By Neil Bronks By Neil Bronks

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

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

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 cm 23 43

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

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

U-Value  U- Value 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 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

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

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

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

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

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

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.

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

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.

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

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  = m w c w  + m c c c 

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

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 )

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

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 )