Question

Write brief answers.
a. Describe a clinical thermometer. How does it differ from the thermometer used in laboratory?

b. What is the difference between heat and temperature ? what are their units.

c. Explain the construction of a calorimeter. Draw the necessary figure.

d. Explain why rails have gaps at specific distances.

e. Explain with the help of formulae the expansion coefficients of liquid and gas.

Answer 1

a. Clinical thermometer is used in homes. It has a glass tube with a bulb at one end and the other end closed. This bulb and some part of the tube is filled with thermometric liquid, such as mercury or alcohol. The rest of the volume of the tube has vacuum in it. There is a kink near the end of the glass tube which prevents the falling back of the thermometric liquid once it is removed from the hot body under observation.
It is basically used to measure the temperature of humans. A clinical thermometer has a temperature range of only 35 ºC to 42 °C.


b.

Clinical thermometer	Laboratory thermometer
This thermometer is used in homes. It is basically used to measure the temperature of human body.	This thermometer is used to measure the temperature of all things, except the human body.
A clinical thermometer has a temperature range of only 35 ºC to 42 °C.	A laboratory thermometer has a temperature range of -10 ºC to 110 ºC.
It has kink.	It does not have kink.

b.

Heat	Temperature
It is a form of energy which causes in us the sensation of hotness or coldness.	It is measure of the degree of hotness or coldness of an object.
It is measured in joules (J).	It is measure in kelvin (K), Celsius (oC) and Fahrenheit (oF)

c. Calorimeter

A device used for heat measurement is called a calorimeter.

Construction of a Calorimeter

• It consists of a metallic vessel and stirrers. They are made of copper or aluminium.

• The vessel is then kept inside a wooden jacket which contains heat-insulating materials.

• The outer wooden jacket acts as a heat shield, and reduces the heat loss from the inner vessel.

• The outer jacket has an opening through which a mercury thermometer is inserted into the calorimeter.

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d. All solids expand on heating. As rails are made up of steel, these also expand in summers and contract in winters. These expansion and contraction can cause sagging and bending of rails which could derail the trains running on them. Thus, the rails have been provided with gaps at specific distance so as to prevent this bending of rails. These spaces get closer in summers and wider in winters.

e. The formula for liquid expansion or gas is

$$\begin{gathered} V_2=V_1(1+\beta ∆T) \\ \mathrm{or} \\ \beta =\left(\frac{V_2-V_1}{V_1}\right)\frac{1}{∆T} \end{gathered}$$
From the above formula, we can say that

• the volumetric expansion coefficient of a liquid ($\beta$) is defined as the fractional change in the volume of the liquid per degree Celsius (or kelvin) change in temperature.
• the volumetric expansion coefficient of a liquid ($\beta$) is defined as the fractional change in the volume of the gas per degree Celcius (or kelvin) change in temperature at constant pressure. So, $\beta$ is the constant pressure volumetric expansion coefficient in case of gas.