by Maryam Hussain
Is temperature depending on
the mass or size of a body?
Temperature is
a macroscopic characteristic of any system such to which a numerical value can
be assigned at a given time without knowledge of the previous behavior,
history, of the system. Hence the temperature is an intensive property of a
system because its value is independent of the size or extent of a
system and may vary from place to place within the system at any moment.
If we wish to measure the
temperature of an elephant under his left ear and then under his right ear,
then it will be same for both of a 500 kg elephant or for a 700 kg elephant.
Therefore, the temperature of the whole body is not the sum of the
temperatures of the parts of that body. Temperature is a technical term
that is quantifies the amount of internal energy possessed by a substance.
How to define the temperature?
Temperature is defined as the
degree of “hotness” or “coldness” of a body.
We use our sense of touch to
distinguish hot bodies from cold bodies and, on the basis of this
distinguish, we arrange bodies in their order of hotness that body-1 is hotter
than the body-2 and so on.
When a hot body and a cold body
are brought into physical contact, the hot body becomes cooler and the cold
body becomes warmer. If both of these bodies maintain contact with each other for
some time, then both of these bodies will have the same degree of hotness or
coldness.
How temperature travels
through the two contact bodies? What is the basis for temperature detection?
To understand how temperature
travels through the two contact bodies, let us go through the zeroth law of
thermodynamics. This law states that when two bodies have equality of
temperature with a third body, then the two bodies also have equality of
temperature with each other. This zeroth law of thermodynamics is the basis
of temperature measurement.
Whenever a body has
equilibrium of temperature with the thermometer, then we can conclude that the
body has the temperature that we read on the thermometer whether it is a
mercury thermometer or a thermocouple or resistance thermometer.
Anybody that possesses a
measurable property such that this measurable property changes as the
temperature of the same body changes, then this measurable property can be used
as a thermometer & such property is termed as thermometric property.
Therefore, human sense of
feeling of hotness or coldness is definitely a thermometric property. The
materials that exhibits changes in the thermometric property are known as
thermometric materials.
What are parts of a mercury
thermometer?
One such device that exhibits
thermometric property & measures the temperature is a capillary tube filled
with a liquid, previously mercury, and is known as the thermometer.
Because the density of the liquid
decreases with temperature and increases with decrease in temperature, (density
being thermometric property), the height of the liquid column in the
capillary tube increases or decreases when the thermometer measures hot body
temperature or cold body temperature respectively.
The tube is graduated with the
temperature and one reads the temperature of subject from those markings.
Different types of fluids are used in such thermometers, depending on the range
of temperature to be measured.
How to calibrate a fluid tube
thermometer?
We all know that in Celsius
scale, the freezing point of water saturated with air at standard atmospheric
pressure) is zero degree and at this point we can have both ice or water at
ambient atmospheric pressure. Also, the boiling point of pure water at standard
atmospheric pressure is 100 Celsius. Therefore, if we have ice and boiling
water at atmospheric pressure, we can calibrate a thermometer.
We can give a numerical scale to
a thermometer by immersing it in an ice bath and making a mark for zero
at the fluid (mercury) level in the thermometer. We can also give a
numerical scale to a thermometer by immersing it in boiling water and making
a mark for 100 at this greater fluid (mercury) level of thermometer. Now
divide the distance between the two marks into 100 equal spaces called degrees.
Similarly, the other spaces on
the thermometer can also be marked off by giving the equal sizes in between
spaces below zero and above 100; thereby extending the range of the
thermometer. By doing this method of calibration, all thermometers,
regardless of the type or composition of fluid, provide the same reading at
zero Celsius and at 100 Celsius.
What are the dynamics of
temperature for a normal human body?
A normal human body temperature
changes throughout the day; generally, it is lowest in the morning and, highest
in the evening. Different parts of the human body also have
different temperatures. Therefore, the standards for measuring different
parts of the human body are also different. The human body temperature is
controlled and adjusted by the hypothalamus in the brain.
Body temperature is measured by
means of a thermometer. Mercury thermometers are not usually used due to
environmental concerns. Prefer to use digital thermometers. Common sites to
measure temperature include under the tongue, the armpit, the forehead, or in
the ear. A normal body temperature is between 96.8°F (36°C) and 98.6°F (37°C),
although this can vary slightly from person to person. In a fever, your
body temperature is raised persistently above the normal level of 98.6°F
(37°C).
Which types of thermometer are
used for determining temperatures of different parts of human body?
The option of body temperature
measurement site depends on the model of the thermometer you have. Many vendors
of thermometers are available in market stores. Infrared thermometer is
worth keeping one in a home first aid kit, especially if you have children.
For young children, measuring of temperature either in the ear or in the
vicinity of ear is the quickest and most effective method.
The ear & forehead
thermometer measures the infrared energy emitted from the forehead or eardrum
and then converts it into a temperature value. The ear and forehead
thermometer can also be used for measuring the room temperature and the
temperature of food and fluids etc.
When you use a digital
thermometer to check your body temperature then you should hold it in place
until it beeps, then pull it out & read the temperature display. The
time interval between the beep & reading of the temperature display should
be minimum in order to minimize the loss of heat from the temperature probe
to the surroundings or vice versa.
It is recommended to avoid the
usage of forehead temperature strips because these are not reliable.
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