Download Temperature

Vadodara institute of
engineering
Harshang shah(130800119096)
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.
Zeroth law of thermodynamics.
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
Temperature Scales
 Conversion between two scales:
5
TF  32
9
9
TF  TC  32
5
TC 
 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?
Temperature relathionships
(°F) = 9/5*(°C) +32
(°C) = 5/9*[(°F) –32]
(°F) = (°R) – 459.67
(°C) = (K) – 273.15
Zero Temperature
 The zero point on the
Fahrenheit scale was based on
the temperature of a mixture of
salt and ice in a saturated salt
solution.
 The zero point on the Celsius
scale is the freezing point of
water.
 Both scales go below zero.
 Is there an absolute zero?
What is absolute zero?
 If the volume of a gas is kept
constant while the temperature is
different, the pressure will be
different.
The Third Temperature Scale
 Absolute Temperature Scale (Kelvin Scale)
TK  TC  273.2
 Example

Water freezing point: 0C =273.2 K.
Water boiling point: 100C = 373.2 K
Heat and Specific Heat Capacity
Steel
has a lower specific
heat capacity than water.
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 10.1 Specific capacity of some common substances
Substance
Water
Ice
Steam
Ethyl alcohol
Glass
Aluminum
Specific Heat Capacity (in Cal/g/C)
1.0
0.49
0.48
0.58
0.20
0.215
 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
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).
Phase Change and Latent Heat
 When an object goes through a change of phase or
state, heat is added or removed without changing the
temperature. Instead, the state of matter changes:
solid to liquid, for example.
 The amount of heat needed per unit mass to produce
a phase change is called the latent heat (L)
 The latent heat of fusion of water is 80 cal/g (Lf = 80
cal/g is 80 cal/g): it takes 80 calorie of heat the melt 1 g
of ice at 0C to become water at 0C.
 The latent heat of vaporization of water is 540 cal/g (Lv
= 540 cal/g): it takes 540 calories of heat to turn one
gram of water at 100 C into steam at 100 C.
Heat and Mechanic Energy
 Benjamin Thompson (1753-1814)
noticed that cannon barrels and drill
bits became hot during drilling.
 Joule performed a series of experiments
showing that mechanical work could
raise the temperature of a system.
1 cal = 4.19 J
 First law of Thermodynamics.
Energy Conservation - In an isolated system, the total
amount of energy, including heat, is conserved.
Applying the First Law of Thermodynamics
 Example (Box 10.2) :A hot plate is used to transfer 400 cal
of heat to a beaker containing ice and water. 500 J of work
are also done on the contents of the beaker by stirring.
a) What is the increase in
internal energy of the
ice-water mixture?
b) How much ice melts in
this process?
The Flow of Heat
 Three basic processes for heat flow:
 Conduction
 Convection
 Radiation
Conduction: heat flow when in contact

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.

A metal block at room
temperature will feel colder
than a wood block of the exact
same temperature. Why?
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.