Temperature and its measurement Class 6 Curiosity Notes
Temperature
The degree of hotness or coldness of an object is called its temperature. The SI unit of temperature is Kelvin (K).
Measurement of Temperature
The instrument used to measure temperature is called a thermometer.
Clinical Thermometer:
The commonly used clinical thermometer is made up of a narrow tube (capillary) of thick glass.
At the end of the capillary tube is a thin glass bulb filled with mercury.
Mercury is preferred in thermometers because it is present in liquid state over a wide range of temperatures. It is a silvery grey in colour, therefore it is relatively easy to observe. It does not stick to the glass in which it is enclosed.
The scale in a clinical thermometer extends over a few degrees on either side of the normal body temperature of 37 degree Celsius.
It can measure temperature from 35 degree Celsius to 42 degree Celsius.
The clinical thermometer is marked to indicate a small change of 0.2 degree Celsius.
The capillary tube of a clinical thermometer has a kink or bend that does not allow the mercury to flow back into the bulb before the temperature has been read.
To lower the level of mercury, the thermometer has to be given a firm jerk.
While using a clinical thermometer, the following precautions should be taken:
The thermometer should be washed before and after use preferably with an antiseptic solution.
The thermometer should be read keeping the level of Mercury along the line of sight.
It should be handled with care.
The bulb of the thermometer should not be touched while taking a reading. Hold the thermometer by its glass body.
It should be ensured that before use, the mercury level is below 35 degree Celsius or 95-degree Fahrenheit.
Digital thermometer:
Nowadays, digital thermometers are used to measure body temperature.
They work on tiny dry cells.
It is a safer device because it does not contain mercury which is a toxic substance.
Laboratory thermometer:
A laboratory thermometer is made up of a glass tube.
It has a glass work with mercury which on gaining heat rises in the glass capillary of the tube.
The range of temperature that laboratory thermometers can measure is between -10 degree Celsius to 110 degree Celsius.
The following are some precautions to be taken while using a laboratory thermometer:
Handle the thermometer with care.
Do not hold the thermometer by the bulb while taking a reading.
The thermometer should be kept upright, not tilted. The bulb should not touch the surface of the container.
Removing the thermometer from a boiling water bath and immediately immersing it in an ice bath may cause the thermometer to break.
Temperature Scales
Temperature is measured using different temperature scales. In a temperature scale two reference temperatures are chosen (most commonly the freezing and boiling point of water). The commonly used scales are the Celsius scale the Fahrenheit scale and the Kelvin scale.
Celsius scale:
Around 1743, Anders Celsius invented the Celsius scale. He determined the freezing temperature for water to be at 0 degree and the boiling temperature at 100 degrees. There are 100 divisions between these two points.
Fahrenheit scale:
This scale was developed by Daniel Gabriel Fahrenheit. The unit of this scale is degree F.
On this scale, the freezing point of water is taken as 320 Fahrenheit and the boiling point of water is taken as 2120 Fahrenheit. There are 180 divisions between these two points.
Kelvin scale:
This scale was invented by Lord kelvin. The unit of the scale is K. On this scale, the freezing point of water is taken as 273 K and the boiling point of water is taken as 373 K.
Temperature scale
Boiling point of water
Freezing point of water
Degree Fahrenheit
212
32
Degree Celsius
100
0
Kelvin
373
273
Conversion of Scales:
The three temperature scales (Celsius, Fahrenheit and Kelvin) can be converted from one to the other, using the following formula:
$T_F=\frac {9}{5} T_C+ 32^0$
$T_C=T_K−273.15$
