Temperature and Its Measurement G7

CHAPTER 2 TEMPERATURE AND ITS MEASUREMENT.

A. THE DEFINITION OF TEMPERATURE.
Temperature is the relative measurement (degree) of hotness or coldness of an object or a system. To measure the temperature you cannot use touch-sensory organ, because the result is relative, it means something depend on reference that used, and qualitative.
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B. THERMOMETER.
The word thermometer come from the word thermos meaning warm and meter meaning measuring device. Etymologically, the thermometer is a device used to measure the temperature
appropriate and expressed it by a number.
Thermometer is made according to the properties of a substance which can change in volume if it undergoes the change of temperature. For example, the air in a balloon/closed platisc if it is
dipped in the hot water, the air in the balloon/plastic will expand so the balloon/plastic develops.

Thermometer is commonly made of a glass tube which is filled with liquids. The liquids
are used as a thermometer filler, because the liquids undergo the change in volume if the temperature changes.

Commonly, thermometer at it is now use alcohol and mercury to fill their tubes, because alcohol and mercury have superiorities compared with anothers. However, there are also the
weaknesses of alcohol and mercury. Meanwhile, the superiorities and weaknesses of alcohol and
mercury are as follows.
The superiorities of alcohol :
a. It can measure a low temperature, because its freezing point is low ( - 1150C ).
b. It can measure the temperature precisely, because it has large expansion coefficient.
c. Its expansion is regular.

The weaknesses of alcohol :
a. It cannot measure a high temperature, because its boiling point is low ( 780C ).
b. It makes wet the wall of its place.
c. It is colourless so it must be given dyestuff in order to be visible.
d. Its special heat is high so needs energy is large for increase the temperature.

The superiorities of mercury :
a. It is visible, because its colour is silvery shining.
b. Its expansion is regular.
c. It does not make wet the wall of its place.
d. It can measure a high temperature, because its boiling point is high ( 3570C )
e. It can measure the temperature quickly and precisely, because easy adapt with the temperature surround it.

The Weaknesses of Mercury :
a. It can not measure very low temperature, because its freezing point is high ( -400C ).
b. Mercury is poisonous, so it is harmful if its tube is broken.
c. Its price is very expensive.


C. THERMOMETER CALIBRATION.
Thermometer calibration is an activity to fix the thermometer scale by using the certain marks. There are four steps to calibrate a thermometer, those are :
1. Determine the lower fixed point .
Usually the lower fixed point of a thermometer is the freezing point ( melting point ) of pure water at 1 atm pressure and it is used as measurement reference of the lowest temperature of the thermometer. For example , the under fixed point of a Celcius thermometer is marked with scale of zero ( 00C ).
2. Determine the upper fixed point.
Usually the upper fixed point of a thermometer is the boiling point of pure water at 1 atm pressure and it is used as measurement reference of the highest temperature of the thermometer.
For example, the upper fixed point of the Celcius thermometer is marked with scale of 100.
3. Devide the distance between the under fixed point and upper fixed point on the thermometer in-
to several same parts. For example, a Celcius thermometer is devided into 100 parts and each part is 10C.
4. To obtain the better range of measurement, then the thermometer scale can be extended by fixing the scale below the under fixed point or above the upper fixed point.


D. THE KINDS OF THERMOMETER SCALE.
In physics, there are four kinds of scale which usually used in the measurement of temperature, those are Ceicius, Fahrenheit, Kelvin, and Reamur scales. The following are explanations about the four scales of thermometer.
a. Celcius scale.
In celcius scale, the under fixed point is marked with number 00C and the upper fixed point is marked with number 1000C. This scale proposed by Anders Celcius ( 1701 – 1744 ) by fixing the melting point of ice as the under fixed point and the boiling point of water as the upper fixed point.

b. Fahrenheit scale
Fahrenheit scale was proposed by German physicist, Daniel Gabriel Fahrenheit ( 1686 -1736 ). In Fahrenheit scale, the under fixed point is marked with number 320F and the upper fixed point is marked 2120F. Fahrenheit fixed the upper fixed point and under fixed point based on freezing point and boiling point of pure water at 1 atm pressure.

c. Kelvin scale
Kelvin scale was proposed by England physicist, Lord William Thomson Kelvin ( 1824- 1907 ). In Kelvin scale, the under fixed point is marked with number 273 K and upper fixed point is marked 373 K. Measurement of temperature in Kelvin scale is based on the absolute zero temperature, read the following explanation.
Every substance consists of particles that vibrate, and the vibration of the particles producing the kinetic energy. The average kinetic energy of paticles of a substance is proportional with the substances temperature. If the substance is getting warmer, it means the average kinetic energy of particles is also increasing. Thus, temperature is the measure of average kinetic energy of a substance particles.
The kinetic energy and speed of particles of a substance is decreasing along with the decrease of temperature, and when the temperature reaches approximately – 273.160C, the particles motion stop, therefor no more temperature can be measured. This temperature is the lowest temperature of an object and is called the absolute zero temperature and the lowest temperature in the Kelvin scale is marked 0 K which equal to – 273.160C.

d. Reamur scale
In the Reamur scale, the under fixed point is marked with number 00R and upper fixed point is marked 800R. The under fixed point is obtained from the melting point of pure ice and the boiling point of pure water as the upper fixed point at pressure of 1 atmosphere of the air.

The relationship of Celcius, Kelvin, Reamur and Fahrenheit scales.
The quotient difference of upper and under fixed point of scale C, K, R, and F is C : K : R : F = 100 : 100 : 80 : 180 can be simplified C : K : R : F = 5 : 5 : 4 : 9
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