CHAPTER 6
Temperature
and Heat
Learning outcomes
the students will be able to:
· 1. Define temperature, heat, heat capacity, specific heat
capacity and its unit.
· 2.Describe the process of heat transfer.
· 3.Apply the concept and formula in solving problems on
specific heat capacity.
· 4.Calculate heat energy transferred between two objects
at different temperature.
· 5.Determine temperature at thermal equilibrium.
*Mahtab Narsimhan*
INTRODUCTION
Temperature and heat are related to
each other, but are different concepts. The temperature of an object is a measure of how
hot or cold it is. However, determining the temperature can be quite
subjective, different people will have different perceptions of what is hot and
what is cold. In simple terms temperature is said to be the degree of hotness. While, heat is the transfer of energy from a hot object to a colder object. More
scientifically, it is the potential
for heat transfer by conduction,
convection or radiation. A
temperature difference causes heat to flow, just as a voltage causes a current
to flow in a wire. If two objects are placed in contact, heat will flow from the hotter to the colder. When no more heat
flows, the object are at thermal
equilibrium and their temperatures are same.
Temperature,
T
Temperature
is a number that is related to the average kinetic energy of the molecules of a
substance. The number is measuring of
hotness and coldness of a substance, body or environment. Temperature is not an energy.
Heat
|
Temperature
|
|
Definition
|
Heat
is an energy that is transferred from one body to another
|
Temperature
is a measure of hotness or coldness
|
Physical Quantity
|
Derived quantity
|
Base quantity
|
Symbol
|
Q
|
T
|
Unit
|
Joules
|
Kelvin,
Celsius or Fahrenheit
|
SI unit
|
Joules
|
Kelvin
|
Ability
to do work
|
Heat has the ability to do work.
|
Temperature
can only be used to measure the degree of heat.
|
Measuring device
|
Thermometer
|
No
specific measuring equipment
|
THE
PROCESS OF HEAT TRANSFER
Heat transfer is the movement of thermal energy
from one thing to another thing of different
temperature. These objects could be two solids, a solid and a liquid or
gas, or even within a liquid or gas. The method of
heat transfer are conduction, convection and radiation. Both conduction and convection
require matter to transfer heat.
Conduction
Conduction
is the heat transfer through one substance to another through direct contact. Conduction occurs
because molecules in a hotter region transfer energy to those of an adjacent
cooler region through collisions.
This method of heat transfer apply in a solid material
which called conductor. Most metals are good conductors because they
easily transmit heat energy by conduction. Bad
conductors are called insulators because
they do not easily transmit heat by conduction example wool, wood, most liquids
and gases.
Examples of conduction are metal spoon in a pan of hot soup, putting your hand
on a stove burner and transfer energy from the stove to the food in pots and
pans.
6.2.2
Convection
Convection is the up and
down movement of molecules within fluids (i.e. liquids and gases) caused by
heat transfer. Convection
occurs when warmer areas of a liquid or
gas rise to cooler areas in the liquid or gas because a
fluids becomes less dense when heated and therefore rises. Cooler liquid or gas
then takes the place of the warmer areas which have risen higher. This results
in a continuous circulation pattern. Figure 6.5 show water boiling in a pan
applying convection method. Examples of convection hot air balloon, and warmer
water at the surface of lake or swimming pool. Another good example of convection
is in the atmosphere. The earth's surface is warmed by the sun, the warm air
rises and cool air moves in.
6.2.2
Radiation
Radiation is an
energy transferred when electromagnetic
waves travel through empty spaces. When electromagnetic waves come in
contact with an object, the waves transfer the heat to that object. Radiation
is a method of heat transfer that does
not rely upon any contact between the heat source and the heated object as
is the case with conduction and convection. Heat can be transmitted though empty space by thermal radiation often
called infrared radiation. No medium is required in the process of radiation.
Examples of radiation are the heat from the sun, heat released from the
filament of a light bulb, camp fire, electric heater, microwave oven.
HEAT CAPACITY
The heat
capacity of an object is the amount
of heat required to increase the temperature of the object by 1 °C. Each
object has its own heat capacity
Specific Heat Capacity
The specific heat capacity of a substance
is the amount of heat energy required to
increase the temperature of 1kg of the substance by 1 °C or 1 K. The SI
unit for specific heat capacity is J kg-1
°C-1 or J kg-1
K-1 and the symbol is, c
Substance
|
Specific heat capacity, c
(J kg-1 °C-1 )
|
Substance
|
Specific heat capacity, c
(J kg-1 °C-1 )
|
Substance
|
Specific heat capacity, c
(J kg-1 °C-1 )
|
|
Solids
|
Liquids
|
Gas
|
||||
Ice
|
2100
|
Water
|
4200
|
Steam
(110 °c)
|
2010
|
|
Aluminum
|
900
|
Alcohol
|
2400
|
|||
Concrete
|
800
|
Paraffin
|
2100
|
|||
Glass
|
837
|
Mercury
|
140
|
|||
Iron
|
500
|
|||||
Copper
|
387
|
|||||
THERMAL EQUILIBRIUM
Thermal equilibrium is a condition in which there is
no net heat flow between two objects that are in thermal contact with each
other. When two objects of different temperatures are placed in contact
with each other, the object with the higher temperature will transfer heat
to the object with a lower temperature. After a while, both objects will
attain the same temperature. At this state, both objects have reached
thermal equilibrium. Then the two objects in thermal equilibrium with each
other are at the same temperature. Conversely, if two objects have different
temperature, they are not in thermal equilibrium with each other.
Formula of energy
ReplyDelete