Why is the thermometer not dipped in water while fixing its upper fixed point?
Answers
Answer:
In physics we need to quantify temperature. A calibrated thermometer, a mercury-in-glass thermometer for example, allows us to obtain temperature readings from its markings. Liquid-in-glass thermometers make use of the property that liquids, usually mercury or coloured alcohol, expand in a glass tube in response to a rise in temperature. But have you ever wondered how the markings on a thermometer are set? For that you need to know how to define a temperature scale.
Fig. 1-3 Mercury-in-glass thermometer (upper) and Alcohol-in-glass thermometer (lower).
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Temperature scale
Fig. 1-4 The upper and lower fixed points are defined as the boiling temperature of pure water and melting temperature of pure ice respectively.
Fig. 1-5 The temperature of pure melting ice is 0oC.
To define a temperature scale, we first choose two reference temperatures called the fixed points. In some commonly used temperature scales, for example the Celsius scale, the fixed points are defined using the following properties of pure water:
The lower fixed point, or ice point, is the temperature of pure melting ice at normal atmospheric pressure.
The upper fixed point, or steam point, is the temperature of pure boiling water at normal atmospheric pressure.
Note that the fixed points are defined using common physical phenomena so that they can be easily reproduced. When pure water boils at normal atmospheric pressure, its temperature must be equal to the upper fixed point; it does not matter if we are heating water in the laboratory with a Bunsen burner or in the kitchen with a stove. Similarly the lower fixed point can also be easily reproduced.
Once we have two fixed points, we can define a temperature scale. In the Celsius scale, the range between the lower and upper fixed points is divided into 100 divisions, each called a degree Celsius, written as . The lower fixed point is taken as 0 and the upper fixed point is taken as 100 .
You can easily calibrate a liquid-in-glass thermometer to the Celsius scale, look at the following animation and try this in the activity.
Explanation:
Explanation:
Thermal Properties of Matter
The upper and lower fixed points of a faulty mercury thermometer are 210oF and 34oF respectively. The correct temperature
C
100oF
180F−32=U−LF−L
180F−32=210−34F−34
180F−32=176F−34
45F−32=44F−34
45F−45×34=44F−44×32
45F−44F=1530−1408
F=122