1. CHAPTER ELEVEN:
THERMAL PROPERTIES OF MATTER:
The following points are to be discussed:
Temperature and heat
Measurement of temperature
Ideal-gas equation and absolute temperature
Thermal expansion
Specific heat capacity
Calorimetry
Change of state
Heat transfer
Newton’s law of cooling
2. Heat:
► Heat is that form of energy that flows from one body to
another body or its surrounding due to difference in
temperature.
► (Note only that energy which flows from one point to
another due to difference in temperature is heat.)
► Heat is measured in Joule/Calorie/kilocalorie.
3. Temperature:
► Temperature is measure of degree of hotness or coldness of
body.
► The S.I. Unit of Temperature is Kelvin (K) and some of the
commonly used units are: Fahrenheit (°F) and Celsius (°C).
4. Measurement of temperature
1. To measure temperature the change that takes place due to temperature
change is measured.
2. Any phenomenon in nature which takes place at a particular temperature is
taken as reference.
3. For the definition of any standard scale, two fixed reference points are
needed.
4. The ice point and the steam point of water are two convenient fixed points
and are known as the freezing and boiling points. These two points are the
temperatures at which pure water freezes and boils under standard pressure.
5. Measuring temperature
Temperatures in
everyday
situations are
usually measured
in degrees Celsius
(oC) – also
referred to
sometimes as the
‘centigrade scale’.
Two fixed points
0oC, the freezing
point of pure
water.
100oC, the
boiling point of
pure water.
6.
7.
8. Natural phenomena Celsius Fahrenheit Kelvin
Boiling point of water 1000 C 2120F 373.15
Freezing point of water 00 C 320F 273.15
Number of divisions in the
scale between boiling point
and freezing point.
100 180 100
Any random phenomena
temperature in different scale.
C F K
Natural phenomena in different Scale
9.
10. This is because the slope of the graph is constant between
two scales A and B.
11. Ideal-gas equation and absolute
temperature
An equation which relates pressure P, temperature T and volume V of a gas is
called gas equation.
Those gases which follow the ideal gas equation are called ideal gas, but in actual
practice the gases behavior varies such gases are called real gas.
The ideal gas equation is represented as-
PV=µRT
Where P= Pressure of the gas
V= Volume of the gas
µ = Number of moles of the gas
R = a constant called gas constant
T = Temperature in Kelvin scale
12. When we put this in above equation-
PV=µR( t+273.15)
The graph between P &t and P & V is given –
15. Thermal Expansion of a body
► Change in dimension of a body due to change
in temperature
16. Thermal Expansion of a body
► The expansion in length is called linear expansion.
► The expansion in area is called area expansion.
► The expansion in volume is called volume expansion.
19. Coefficient of Area Expansion
► If the substance is in the form of a
sheet, then for small change in
temperature ΔT, fractional change
in area ΔA/A is directly proportional
to temperature change ΔT.
= βΔT
Where β is called Coefficient of Area
Expansion
20. Coefficient of Volume Expansion
► For small change in temperature ΔT,
fractional change in volume ΔV/V is
directly proportional to temperature
change ΔT.
= γΔT
Where γ is called Coefficient of
Volume Expansion
21. Thermal Expansion - applications
Thermometer
Mercury
or alcohol
Expanding
liquid
Calibration scale
As the temperature
rises, the liquid in the
bulb expands, and so
rises up the narrow
tube which is
calibrated to fixed
points (eg. 0oC, 100oC)
Bimetallic strip
In a bimetallic strip, a low
expansion metal (eg. Invar) is
bonded to a high expansion metal
(eg. Brass). As the strip is heated,
the brass expands more than the
invar, causing the strip to bend.
http://www.schoolphysics.co.uk/age11-14/Heat%20energy/Expansion/text/Expansion_of_solids/index.html
