The Fahrenheit and Celsius scales use different numerical
values for the freezing and boiling points of water. The
Celsius degree is larger than the Fahrenheit degree.
Temperature:
For objects #1 and #2 which are brought in contact, heat
will flow from object #2 into object #1 if T2 > T1.
Fahrenheit:
TF = (9/5)TC + 32
Celsius:
TC = (5/9)(TF - 32)
Kelvin:
TK = TC + 273.2
Zero K = “absolute zero”;
No physical system can get colder than this.
The pressure plotted as a function of temperature
for different amounts of different gases. When
extended backward, the lines all intersect
the temperature axis at the same point.
One-hundred grams of room-temperature water (20°C)
is more effective than 100 grams of room-temperature
steel shot in cooling a cup of hot water.
Specific Heat Capacity:
How much heat is needed to increase the temperature of one gram of
water by one degree C?
Exactly 1 Calorie. 1 cal = 4.186 J (energy)
Hence, the specific heat capacity is:
Water 1.0
cal/gm/C
Ice
0.49
Steel 0.11
It takes much less heat to raise the temperature of 1 gram of steel
than 1 gram of water. Steel will not remove as much heat from your
hot coffee; water is a better cooling agent.
What is heat?
It is the energy that flows from a hot
object to a cooler one.
Heat flows from the hotter object to the colder
one when two objects at different temperature
are placed in contact. The changes in temperature
that result depend on the quantities of material
and the specific heat capacity of each object.
Adding heat to a mixture of water and ice at 0°C melts
the ice without changing the temperature of the mixture.
Will adding heat to a body always raise its
temperature?
No, there can be a change of phase.
It takes 0.49 cal to raise 1 gram of ice from -1 C to 0 C.
But, it takes another 80 cal to go from ice at 0 C to water
at 0 C.
Similarly, it takes 540 cal to go from 1 gram of water at
100 C to one gram of steam at 100 C.
A falling mass turns a paddle in an insulated beaker of
water in this schematic representation of Joule’s
apparatus for measuring the temperature increase
produced by doing mechanical work on a system.
An object can get hotter by
• adding heat to it
• doing work on it!
Total energy is conserved. Heat is another
form of energy.
Lecture Quiz 21 - Question1:
A beaker contains liquid water plus ice. Some time later,
the ice is melted. One can conclude that:
A. Heat must have been added to the beaker.
B. Cold must have flowed out of the beaker.
C. Work had to be done on the beaker.
D. The amount of energy in the beaker increased.
E. More than one of the above.