Temperature is the degree of hotness or coolness of a body. The hotter the body is higher is its temperature.

**Concept
of temperature**

Temperature is the
degree of hotness or coolness of a body. The hotter the body is higher is its
temperature.

The SI unit of
temperature is *kelvin***(K)**. For day to day applications, ** Celsius**
(˚C) is used. Temperature is measured with a thermometer.

There are three scales
of temperature.

i.
Fahrenheit scale

ii.
Celsius or Centigrade scale

iii.
Kelvin or Absolute scale

In Fahrenheit scale, 32
˚F and 212 ˚F are the freezing point and boiling points respectively. Interval
has been divided into 180 parts.

In Celsius scale, also
called centigrade scale, 0˚C and 100 ˚C are the freezing point and boiling
respectively. Interval has been divided into 100 parts. The formula for
converting a Celsius scale to Fahrenheit scale is:

The formula for converting
a Fahrenheit scale to Celsius scale is:

Kelvin scale is known as
the absolute scale. On the Kelvin scale 0 K represents absolute zero, the
temperature at which the molecules of a substance have their lowest possible
energy. The solid, liquid, gaseous phases of water can coexist in equilibrium
at 273.16 K.

*Kelvin is defined as
1/273.16 of the triple point temperature.*

The formula for
converting a Celsius scale to Kelvin scale is:

K = C + 273.15

The formula for
converting a Kelvin scale to Celsius scale is:

C = K - 273.15

**Absolute zero**

The temperature at which
the pressure and volume of a gas theoretically reaches zero is called absolute
zero. This is shown in Figure 1.8.

For all gases, the
pressure extrapolates to zero at the temperature -273.15 ˚C. It is known as
absolute zero or 0 K. Some base line temperatures in the three temperature
scales are shown in Table 1.1.

i. 25 ºC to Kelvin

ii. 200 K to ºC

i. (T_{K}) = (T°_{C})
+ 273.15

(T_{K}) = 25 +
273.15 = 298.15 K

ii. (T°_{C}) =
(T_{K}) - 273.15

(T°_{C}) = 200 -
273.15 = -73.15 ºC

**Convert the following**

i. 35°C to Fahrenheit
(°F)

ii. 14° F to °C

i. T(°F) = T(°C) × 1.8 +
32

T(°F) = 25° C × 1.8 + 32
= 77° F

ii. T(°C) = (T(°F) –
32)/ 1.8

T(°C) = (14°F – 32)/ 1.8
= -10° C

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9th Science : Heat : Concept of temperature |

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