Heat
By
Neil Bronks
Thermometers
Three things that make up a thermometer
Fixed Point
Thermometric
Property
Something
that varies
Measurably with
temperature
---------------------
Usually the
boiling point
and melting points
of water
Scale
Divisions between
the fixed points
Different Thermometers
Thermocouple
Junction emf
Emf
Platinum Wire
Resistance
R
Temp
CVGT
Pressure
Pressure
Temp
Temp
The only linear thermometric property is the CVG.
All the others must be calibrated to the CVG
CALIBRATION CURVE OF A THERMOMETER USING
THE LABORATORY MERCURY THERMOMETER AS
A STANDARD
Mercury thermometer
Boiling tube
Alcohol
thermometer
uncalibrated
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
Heat Transfer
Conduction
-Transfer
by
vibrations
Convection
-Hot air
rising
carrying
the
heat up
with it.
Radiation
-Transfer by
Electro-magnetic wave
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 1m2 where the
temperature difference is 1k
Radiation
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
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
Boiling
point
Heat raises
temperature
Energy=mcΔθ
Melting
point
Gas
Boiling
Liquid
Melting
Solid
Latent Heat
Only
Energy=ml
Time
The Refrigerator
Gas
turns
back
into a
liquid
giving
out
heat
Liquid
Gas
Compressor
Liquid
boils
and
takes in
Latent
Heat
from
the
food
Heating Up
Heat that raises temperature
Energy Supplied=mcΔθ
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
Amount of heat energy
to change state of1kg
without changing temp.
MEASUREMENT OF SPECIFIC HEAT CAPACITY OF
WATER BY AN ELECTRICAL METHOD
10°C
12 V a.c.
Power supply
Joule
meter
350 J
Cover
Digital
thermometer
Water
Lagging
Calorimeter
Heating coil
Electrical energy supplied = energy gained by (water +calorimeter)
Q
Precautions
=
mwcw θ
+ mcalccal. θ
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
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 = mw cw + mc cc
MEASUREMENT OF THE SPECIFIC LATENT
HEAT OF FUSION OF ICE
10°C
Wrap ice in
cloth to
crush and
dry.
Crushed
ice
Calorimeter
Digital
thermometer
Water
Lagging
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)
MEASUREMENT OF THE SPECIFIC LATENT
HEAT OF VAPORISATION OF WATER
10°C
Steam
Trap
Digital
Thermometer
Lagging
Water
Calorimeter
Heat
source
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)