Measurements

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1.general physics  1.1 length and time  -i-Physical Quantity Physical Quantities A physical quantity is a property of an object that can be measured with a measuring instrument. A physical quantity is usually expressed as “a magnitude ( numerical value)  and a  physical unit or more ” Example :- Normal body temperature of a healthy human being is  37  0 C -ii-Length Measuring Length. Length is “the distance between two points in a space”. According to SI units, the length quantity is expressed in meter. There are several kinds of measuring devices used to measure quantity of length, among others, are as follows. Tools used… a-   Measuring tape. b-   Ruler c-   Vernier callipers. d-    Micrometer Measurement of length Length is measured accurately through many meth...
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Measurement of temperature

Measurement of temperature 


A physical property that varies with temperature may be used for measurement of temperature for example: -liquid-in-glass thermometer: the property is thermal expansion. As temperature rises or falls, the liquid (mercury or alcohol) expands or contracts. The amount of expansion can be matched to a temperature on the scale. 

Fixed point 

Fixed points are definite temperatures at which something happens (when pure water freezes/ice melts: the lower fixed point or ice point and when pure water boils: the upper fixed point or steam
point) which are used to calibrate a thermometer.



Sensitivity:
To increase the sensitivity of thermometers you have to put the liquid in a narrowertube. This makes more distance for same amount of expansion of liquid. Mercuryexpands less than alcohol. Sensitivity can be increased by using a material thatexpands more during a temperature change.

•Range:
The maximum and minimum temperature of thermometers
Mercury = -39 °C to 500 °C
Alcohol = -115 °C to 68 °C




Linearity:
If the sizes of the individual degrees are closer to each other then it is more linear 


Thermometer thermocouple 

The probe contains 2 different metals joined metals to form 2 junctions. The temperature difference causes a tiny voltage which makes a current flow. A greater temperature difference gives a greater current. Thermocouple thermometers are used for high temperatures which change rapidly. They have a large range (-200C° to 1100°C) and can be connected to electrical circuits or a computer. 




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