medical phycis

1. HEAT

2. Heat
• Heat is a form of energy associated with
vibration of molecules.
• Molecules are always in a state of motion,
which is increased as a body gains heat and
reduced as it loses heat. the motion would
cease only if the body were devoid of heat
energy.

3. Heat and Temperature
Heat:
Heat is the energy that flows from one object to another
when there is a difference in temperature between the
objects. Heat is the average kinetic energy of atoms or
molecules making up the system.
Temperature:
Temperature is an indication
of whether or not and in which
direction, the heat will flow
(Temperature is an indication
of the average of kinetic energy
of atoms or molecules).

4. Temperature
• Temperature is the thermal condition of a body
which determines the interchange of heat
between it and other bodies.
• It may be regarded as the level of heat, as heat
tends to pass from an object at higher
temperature to an object at a lower temperature,
in the same way as water flows from high level to
low level
• The temperature of a body depends on the
quantity of heat that it contains and on the
thermal capacity, or the ability to hold the heat.

5. Temperature and Its Measurement
• How do we measure temperature?
• Thermometer: Device with a physical property
that changes with temperature and can be easily
measured quantitatively.
• If two objects are in contact with one another long
enough, the two objects have the same
temperature (thermal equilibrium).
• Two or more objects in thermal equilibrium have
the same temperature.

6. 6
Temperature Scales & Temperature
Conversions
There are 3 ways to measure temperature:
• Fahrenheit
• Centigrade (or Celsius)
• Kelvin
of 20

7. Temperature Scales
• The first widely used temperature
scale was devised by Gabriel
Fahrenheit.
Water freezing point: 32F
Water boiling point: 212F
• Another widely used scale was
devised by Anders Celsius.
Water freezing point: 0C.
Water boiling point: 100C

8. Temperature Scales
• Conversion between two scales:
• E1. An object has a temperature
of 45C. What is its temperature
in degree Fahrenheit?
• E2. The temperature of a winter
day is 14F. What is the
temperature in degree Celsius?

TC 
5
9
TF  32
 
TF 
9
5
TC  32

9. The Third Temperature Scale
• Absolute Temperature Scale (Kelvin Scale)
• Example
Water freezing point: 0C =273.2 K.
Water boiling point: 100C = 373.2 K

TK TC 273.2

10. Measurement of heat
• The unit for measuring the quantity of heat is taken as
that amount of heat necessary to raise the
temperature of a body of unit weight by unit amount.
• Calorie: 1 calorie is the amount of heat required to
raise the temperature of 1 gram of water through 1 *C
• British Thermal Unit (BThU) : is the amount of heat
required to raise the temperature of 1 lb of water
through 1 * F.
• Specific Heat: the specific heat of a substance is the
quantity of heat required to raise the temperature of 1
gram of that substance through 1 * C.

11. Specific Heat Capacity
• Specific heat capacity (c):
• the quantity of heat needed to change a unit mass (1 g) of
the material by a unit amount in temperature (1 C).
It is a property of the material, determined by experiment.
– The specific heat capacity of water is 1 cal/gC
Table: Specific capacity of some common substances
Substance Specific Heat Capacity (in Cal/g/C)
Water 1.0
Ice 0.49
Steam 0.48
Ethyl alcohol 0.58
Glass 0.20
Aluminum 0.215

12. • When a material’s temperature is changed, we can
calculate how much heat absorbed/released by the
material:
Q = mcT
where Q = quantity of heat
m = mass
c = specific heat capacity
T = change in temperature
Example: E6
How much heat is required to raise the temperature of
70g of water from 20C to 80C

13. Changes in States
melting
Boiling
CONDENSATION
FREEZING
Solid
Gas
Liquid
Gain in heat
Loss in heat

14. Specific Latent Heat
• This is the heat absorbed or released when 1
kg of the substance undergoes a change in
state.
• There are 2 types of specific latent heat:
Specific latent heat of fusion
Specific latent heat of vaporization

15. Specific Latent Heat of Fusion
• This is the heat required by 1 kg of a
substance to change from solid to liquid or
vice versa without a change in temperature
• Formula: Lf = mlf
• Unit: Jkg-1

16. Specific Latent Heat of Vaporisation
• This is the heat required by 1 kg of a
substance to change from liquid to gas
or vice versa without a change in
temperature
• Formula: Lv = mlv
• Unit: Jkg-1

17. The Flow of Heat
• Three basic processes for heat flow:
–Conduction
–Convection
–Radiation

18. – A metal block at room
temperature will feel colder
than a wood block of the exact
same temperature. Why?
 The rate of heat flow depends on:
a) the temperature difference between the objects.
b) the thermal conductivity of the materials, a
measure of how well the materials conduct heat.
Conduction: heat flow when in contact

19. Convection: heat is
transferred by the
motion of a fluid
containing thermal
energy.
Radiation, heat energy is
transferred by electromagnetic
waves.
can take place across a vacuum.

20. 20
Melting
• Melting is a change of state from solid to
liquid.
• Melting occurs at a fixed temperature.
• This temperature is known as the melting
point of the substance.
• Eg. Melting point of water is 0oC or 273 K

21. Effect of impurities of melting point
• Impurities have a great effect on the melting
point of compounds. Because of them, they
cause the melting point to deviate from the
standard. It actually lowers it, because
impurities decreases the quality of a material

22. 22
Boiling
• Boiling is a change of state from liquid to gas.
• Boiling occurs at a fixed temperature. During boiling,
temperature remains constant.
• Heat is taken in / absorbed during this process.
• This temperature is known as the boiling point of the
substance.
• Liquid will remain at boiling point until all the liquid
has changed to gas.

23. Effect of Impurities on Boiling Point
• Adding impurities will raise the boiling point of an object.
• That means to say the liquid will now boil at a higher temperature.
• Pure water should boil at 100˚ Celsius. However, if you add granules
of salt to water before boiling it, the presence of the salt may result in
raising the boiling point of this solution by as much as one or
two degrees Celsius.
The reason why the boiling point of the substance is raised is because
the two components in the solution - in this case, the water and the
salt – form chemical bonds with each other. These bonds require a lot
of energy inorder to break them. In this case, the bonds are being
broken by heat energy, when the solution is heated to temperatures
of over 100˚ Celsius. However, it requires more heat energy
to break the bonds in order to boil the water, than it takes to simply
boil pure water on its own. As more heat energy is required, the
boiling point of the solution increases.