What is Temperature and how is it Measured? Video Lecture | Science Class 7 (Old NCERT)

good morning children today we shall
learn about temperature and how to
measure the temperature
we often say the soup is hot on the ice
cream is very cold but have you ever
wondered what makes the soup hot or the
ice cream cold some objects are hotter
than the other like the soup on the left
side is hotter than the soup on the
right side some objects are colder than
the other like this ice cream is colder
than this cold drink so what makes
things hotter or colder when you get
fever your body becomes hotter than the
normal to know how hot your body has
become your mother puts a thermometer in
your mouth or under the arms temperature
is the quantity that tells us how hot
are cold and object is so the
temperature is degree of hotness or
coldness of a body or a place like the
boiling water is very hot as it has high
temperature and ice cream is very cold
as it has very low temperature when we
put a pot of water on the stove and heat
it it's temperature rises the heat is
form of energy and it is the cause of
temperature it means temperature is an
expression of heat energy hot water
becomes cold when it releases heat so
cold water has lesser heat energy than
the hot water thus coldness is caused by
the absence of heat energy thus when
heat energy flows into the body it warms
up the body and when it flows out of a
body it cools the body
now how to measure temperature when we
touch an object we can say whether it is
hot or cold the sense of touch can
estimate the temperature but we cannot
rely on the touch for the right
measurement of temperature besides we
shouldn't touch things which are very
hot like the boiling water as you may
get burned hence there are instruments
to measure the temperature accurately
which is the thermometer
now the thermometer is used to measure
temperature but what is the unit of
temperature just like we have different
units to measure the length say inch
centimeter meter etc we have different
units to measure the temperature one of
the unit of temperature is degree
Celsius like the temperature on a summer
noon was 41 degrees Celsius the normal
temperature of a human body is 37 degree
Celsius when we have fever
it means our body is hotter than the
normal you must have seen or use the
clinical thermometer used to measure the
body temperature if we look closely you
would find a scale starting from 94 till
108 here F is written besides the scale
f stands for Fahrenheit this is another
unit of temperature and a normal body
temperature is 98.6 degrees Fahrenheit
now let us see the structure of clinical
thermometer it is made of long narrow
uniform glass tube and it has a bulb at
one end which carries the mercury this
mercury expands when we put the
thermometer in the mouth or under
arms to measure the body temperature on
expansion due to the high temperature
the mercury precedes through the narrow
tube like a thread now how to read the
temperature look here the mercury thread
has crossed 102 and has stopped at the
third mark after it there is if we see
the marking after 102 the marking is 104
degrees so 2 degree is divided into 10
parts thus each part is 2/10 which is
equal to 0.2 degree Fahrenheit and thus
the third mark means zero point 2
multiplied by 3 which is 0.6 so we can
say the temperature is 102 degrees plus
zero point 6 degrees which is 102 point
6 degree Fahrenheit so we look at the
Fahrenheit scale on the thermometer to
see where the mercury thread ends and
this is the temperature reading like
here as we saw the reading was 102 point
6 degree Fahrenheit
now if we measure temperature in Celsius
the normal body temperature is 37 degree
centigrade in the clinical thermometer
we can find a Celsius scale starting
from 35 degrees Celsius till 42 degree
Celsius there are different types of
thermometer
besides the clinical thermometer one
type as digital thermometer which
doesn't use mercury we just put the
digital thermometers Pulp in the mouth
or under the arms or touch it with some
object then the screen on
we'll show the temperature reading the
digital thermometer is easier to use and
measures the temperature accurately now
you may wonder can we use the clinical
thermometer to measure the temperature
of boiling water
no the clinical thermometer is just
suitable to measure up body temperature
the temperature of living person cannot
be less than 94 degree Fahrenheit when
the body temperature is less than the
normal it is called hypothermia and when
the body temperature is about the normal
range we call it fever increase in body
temperature is called hypothermia on the
other hand and the chances of survival
of a person are very less if the body
temperature crosses 107 degree
Fahrenheit so the clinical thermometer
has a scale from 94 degree Fahrenheit to
108 degree Fahrenheit but the
temperature of boiling water is 212
degree Fahrenheit or 100 degree Celsius
so if we put the clinical thermometer in
boiling water the mercury would not get
the space to stretch inside the
thermometer and it would crack the
thermometer with the pressure and hence
the clinical thermometer is not used to
measure the temperature of boiling water
you know the laboratory thermometer has
the longer Celsius scale and hence it
can be used to measure higher
temperatures like 80 degree Celsius
hundred degree Celsius and so on so
remember children what is temperature
the temperature indicates the degree of
hotness or coldness of a body or a place
and the temperature is measured in
degree Celsius or degree Fahrenheit and
lastly different types of thermometers
are used to measure
the temperature that's all for now bye
bye children