Heat and Temperature
The measurement of warmness or
coldness of a substance is known as its temperature.
Temperature is a measure of the
average kinetic energy of the particles in an object. It is related to how fast
the atoms within a substance are moving.
Temperature Units:
There are three units which are used to measure the
temperature:
Degree Celsius:
Celsius is written as °C. Celsius is called as Centigrade as well.
Fahrenheit:
Fahrenheit is written as °F.
Kelvin: Kelvin is written as K. The SI unit of temperature is kelvin (K).
Measuring Temperature:
The high temperature means that the
molecules within the object are moving at a faster rate.
In a thermometer, when liquid gets heat, it expands and
when it is cooled down, it contracts. It is used to measure temperature. Like
solid and liquid objects, the effect of heat is also observed on gaseous
objects.
Thermometer:
Thermometer is the most common instrument to measure
temperature.
Why
Mercury or Alcohol is used in Thermometer?
Mostly Alcohol and Mercury are used in thermometers as
they remain in liquid form even with a change of temperature in them. A small
change in the temperature causes change in volume of a liquid. This temperature
change is measured by measuring expansion of a liquid in thermometer.
Types of Thermometers
The commonly used thermometers are clinical thermometers
and laboratory thermometers.
Clinical Thermometer
1.
These thermometers are used to measure the temperature
of a human body, at home, clinics and hospitals.
2.
All clinical thermometers have a kink that
prevents the mercury from flowing back into the bulb when the thermometer is
taken out of the patient’s mouth, so that the temperature can be noted conveniently.
3.
There are
temperature scales on either side of the mercury thread, one in Celsius scale
and the other in Fahrenheit scale.
4.
Since the Fahrenheit scale is more sensitive
than the Celsius scale, body temperature is measured in F only.
5.
A
clinical thermometer indicates temperatures from a minimum of 35°C or 94°F to a
maximum of 42°C or 108°F.
Precautions to be Followed While Using a Clinical Thermometer:-
• The
thermometer should be washed before and after use, preferably with an antiseptic
solution.
• Jerk
the thermometer a few times to bring the level of the mercury down.
· Before
use, the mercury level should be below 35°C or 94°F. Do not hold the
thermometer by its bulb.
• Keep the mercury level along your line of
sight and then take the reading.
•
Handle the thermometer with care. If it hits against some hard object, it may
break.
• Do
not place the thermometer in a hot flame or in the hot sun.
Laboratory Thermometers
1.
Laboratory thermometers are used to measure the
temperature in school and other laboratories for scientific research.
2.
They are also used in the industry as they can
measure temperatures higher than what clinical thermometers can record.
3.
The stem
and the bulb of a lab thermometer are longer when compared to that of a
clinical thermometer and there is no kink in the lab thermometer.
4.
A laboratory thermometer has only the Celsius
scale ranging from −10°C to 110°C.
Precautions
to be Followed While Using a Laboratory Thermometer
• Do not tilt the thermometer
while measuring the temperature. Place it upright.
• Note the reading only when the bulb has been
surrounded by the substance from all sides.
Digital Thermometer
1.
Mercury is a toxic substance and is very
difficult to dispose of if a thermometer breaks. These days, digital
thermometers are available which do not use mercury.
2.
Instead, it has a sensor which can measure the
heat coming out from the body directly and from that can measure the
temperature of the body.
3.
Digital thermometers are mainly used to take the
body temperature.
Caution
A Clinical thermometer has small temperature range. The
glass will crack/ burst due to excessive pressure created by expansion of
mercury.
Scales of Thermometers
Celsius scale
Celsius is the common unit of measuring temperature,
termed after Swedish astronomer, Anders Celsius in 1742, before that it was
known as Centigrade as thermometers using this scale are calibrated from
(Freezing point of water) 0°C to 100°C (boiling point of water). In Greek, ‘Centium’ means 100 and ‘Gradus’ means steps, both words
make it centigrade and later Celsius.
Fahrenheit Scale
Fahrenheit is a Common unit to
measure human body temperature. It is termed after the name of a German Physicist
Daniel Gabriel Fahrenheit. Freezing point of water is taken as 32°F and boiling
point 212°F. Thermometers with Fahrenheit scale are calibrated from 32°F to
212°F.
Kelvin scale
Kelvin scale is termed after Lord Kelvin. It
is the SI unit of measuring temperature and written as K also known as absolute
scale as it starts from absolute zero temperature.
Numerical Problems:-
1.
Q2.
