Transcript Chapter-10 Temperature and Heat

Chapter-10
Temperature and Heat
1 Temperature and First Law of Thermodynamics
2 Heat and Specific Heat Capacity
3 First Law of Thermodynamics
4 Ideal Gas law
5 The Flow of Heat
6 Essay Topic for Final: Global Warming
Body Temperature
Thermometer
Thermometric Property
Mercury thermometer
Length of mercury column
Constant-volume gas thermometer
Pressure of the gas
Thermocouple
Voltage
Ear thermometer
Infrared radiation
The zeroth Law of
Thermodynamics
Consider three systems A, B, & T.
If system A is in thermal equilibrium
with system T and system B is in
thermal equilibrium with system T,
then systems A and B are in thermal
equilibrium with each other.
Thermometer
Standard Temperatures
Calibration
Temperature Conversion
9
Tf  Tc  32
5
Fahrenheit
scale
Celsius
scale
212
100
Unknown
temperature
Tf
Tc
Freezing point
of water
32
0
Boiling point of
water
Absolute Zero
Temperature
Tk  Tc  273
Temp. Conversion Problems
E1 & E4
9
Tf  Tc  32
5
Tk  Tc  273
E1: An object has a temperature of 45°C. What is its temperature
in °F?
E4: The temperature on a warm summer day is 95 degrees F. What
is this temperature
a. In degrees Celsius?
b. In Kelvin?
Heat
Heat is energy that flows from a higher-temperature object
to a lower-temperature object because of the difference in
temperatures.
Units for Heat
SI unit for heat is the joule, J.
Calorie is another unit for heat. It comes with a lower case and an
upper case.
Nutritionists use the word “Calorie,” with a capital C, to specify
the energy content of foods. For example, a regular 12-oz can of
soda has about 140 Calories.
The cgs unit of heat is the calorie, with a lower case. One calorie
(1 cal) is defined as the amount of heat needed to raise the
temperature of one gram of water by one Celsius degree.
1 food Calorie = 1000 calories = 1 kcal
1 calorie = 4.186 J.
Specific Heat Capacity
Specific heat capacity of a material is the quantity of heat
needed to change a unit mass of the material by a unit change in
temperature. It is a property of the material.
Specific Heat Capacities of Some Common Substances
Substance
Water
Ice
Specific heat capacity
[cal/(g. C°)]
1.0
0.49
Steam
Ethyl alcohol
Steel
0.48
0.58
0.11
Aluminum
Lead
0.215
0.0305
Heat Q
The heat Q that must be supplied or removed to change
the temperature of a substance of mass m by an amount
DT is,
Q  mcDT
where c is the specific heat capacity of the substance.
Unit for Specific Heat Capacity:
SI:
J/(kg · C°)
cgs:
cal/(g. C°)
E6: How much heat is required to raise the temperature
of 70 g of water from 20°C to 80°C?
Calorimetry
SP4: A 150-g of a certain metal,
initially at 120°C, is dropped into
an insulated beaker containing 100
g of water at 20°C. The final
temperature of the system is 35°C.
Ignore the heat capacity of the
beaker.
a. How much heat has been
transferred to the water from
the metal?
b. What is the specific heat
capacity of the metal?
Phase Changes: Latent Heat
Latent heat changes the phase of water without changing its temperature.
Latent heat of fusion of water = Lf = 80 cal/g.
Latent heat of vaporization of water = Lv = 540 cal/g.
E8: How much heat must be added to 60-g of ice at 0°C to
melt completely?
The First Law of
Thermodynamics
The internal energy of a system changes from an initial value
Ui to a final value of Uf due to heat Q and work W:
ΔU = Q - W
Ideal Gas Law
PV =NkT
The Flow of Heat
Heat can flow via conduction, convection,
and radiation.
Conduction and Convection
When a metal block and a
wooden block, both at room
temperature, are picked up,
the metal block feels cooler,
due to conduction of heat.
Conduction is the process
whereby heat is transferred
directly through a material.
Convection is the process in which
heat is carried from place to place
by the bulk movement of a fluid.
Thermos Bottle
Radiation
Radiation is the process in
which energy is transferred by
means of electromagnetic
waves.
Heat transfer by radiation can
take place through vacuum.
This is because
electromagnetic waves are
involved in radiation and they
can propagate through empty
space.
Q30: Which heat transfer process is
responsible when heat flows through a
glass windowpane?