This slides contains basic ideas about thermal properties of substance

3.  Temperature is a sensation of hotness or coldness of body.
 temperature is a measure of translational kinetic energy of
system.
 S. I. unit is o
K.
Heat
 Heat is the energy transferred from a body at higher temperature to a
body at lower temperature.
 S. I. unit is Joule.

4. The energy needed to increase the temperature of a
given mass of water by 1 °C is called as calorie.
1 calorie = 4.186 joule.
One kilocalorie of heat is defined as the amount of
heat energy required to increase the temperature of one
kilogram of water through 1 °C.
1 kcal = 4186 J.

5. Absolute Zero and Kelvin Scale
• Temperature is in units called kelvins (K)
• T = 0 K is called absolute zero
• Represents the temperature at which an
ideal gas:
– Has zero volume (at constant pressure)
– Has zero pressure (at constant volume)
K15.273+= CTT CTT ∆=∆

6. Temperature Scales
• Column of fluid
changes height in
response to warmth
or coolness of
surroundings
• Numbers assigned to
the height establishes
the temperature scale
• Each division in the
scale is called a
degreeFig. 10.7,
p.326

7. Temperature Scales
• Defined by:
– Height of column when water freezes (0°C = 32°F)
– Height of column when water boils (100°C = 212°F)
• Note: −40°C = −40°F

9. Conduction
• Conduction is the transfer of heat by the
direct contact of the particle of matter i.e
movement of heating particle.

10. Steady State of Temperature
It is a temperature at which rate of heat absorbed by the
material is equal to the rate of heat evolved.
Temperature Gradient
Temperature gradient is defined as change in temperature per
unit length of rod.
Temperature gradient (T.G.) = ᶿ1 - ᶿ2
o
K/m
d
ᶿ1 = Temperature of layer one
ᶿ2 = Temperature of layer two
d = distance between two consecutive layers.

11. Thermal Conductivity
• The thermal conductivity of a material
describes how well the material conducts
heat.

12. Law of Thermal Conductivity
The amount of heat flowing from C to D at
steady state is directly proportional to
1. Area of cross section of the layer Q α A
2. The temperature difference between the
two layers i.e. Q α (ᶿ1 - ᶿ2 ).
3. Directly proportional to the time for which
the heat flows between the two layers. i.e. t
4. Inversely proportional to distance
between two layers. Q α 1/d
i.e. Q α A. (ᶿ1 - ᶿ2 ). t
d
Q K A. (ᶿ1 - ᶿ2 ). t
=
d
S . I. unit is J/ m o
Ks
c D

13.  Bad conductors of heat such as glass, coal, thermocol, felt, saw dust
are used as insulating material for preserving low temperature.
In safety lamp, flame of lamp is covered with a cylindrical chimney of
iron – gauze which is good conductor of heat.
 Heater are made of good conductor.
 Thermo flask contains doubled walled glass vessel with vacuum
between the walls as conduction can not take place in vacuum.
 Thermal Insulators are used to prevent heat loss to the environment.

14. • Convection is the transfer of heat energy from a
part of body at higher temperature to a part of
body at lower temperature to a part of body
without bodily movement of particle.
– Convection in a gas occurs because gas
expands when heated.
– Convection occurs because currents flow
when hot gas rises and cool gas sink.
– Convection in liquids also occurs because of
differences in density.

15. Convection is directionalConvection is directional

16. Convection
• Convection depends on surface area.
• If the surface contacting the fluid is
increased, the rate of heat transfer also
increases.
• Almost all devices made for convection
have fins for this purpose.
• Convection takes place in liquid

17. Types of Convection
Free Convection/ Natural
Convection
Forced Convection
It occurs due to external agent.
For Example Air Ventilation Through
Open window.

18.  In hot air blower
Electric Fan
 Refrigerator
Air Conditioner
 Ventilation in the room

19. Radiation
• Radiation is heat transfer by
electromagnetic waves.
• It is process of transfer of heat without
necessity of medium.
• Thermal radiation is electromagnetic
waves (including light) produced by
objects because of their temperature.
• The higher the temperature of an object,
the more thermal radiation it gives off.

20. Radiation

21.  Thermal Radiator : Electric Fan, Sun
White cloth absorb less heat so they preferred in
summer.
The bottom of cooking vessels are kept dark and
rough so that they work as good absorber.
Hot water pipes are painted with black color so
they radiate less heat.

22. Convection Radiation
Conduction is the process
of transfer of heat energy
from a part of body at
higher temperature to part
of body at lower
temperature with bodily
movement of particle
Convection is the
transfer of heat energy
from a part of body at
higher temperature to a
part of body at lower
temperature to a part of
body without bodily
movement of particle.
It is the process of
transfer of heat in which
heat is transfer from one
place to other directly
without necessity of
inverting medium.
It is slower process It is medium time consuming It is fastest process
Conduction takes place in
solid
It takes place in liquid and
gases
It takes place in space like
heat radiated from sun.
It require medium It require medium It does not require
medium
Bad conductor of heat such
as glass, coal, thermocole
Hot blower. Electric bulb, sun
Conduction