When a thermometer is taken from the melting ice to a warm liquid, the mercury level rises to \$ \\ \\ \left(\dfrac { 2}{ 5 }\right)^{ th } \$ of the distance between the lower and the upper fixed points. The temperature of liquid in K is

Given:\$T_b-T_f=100\$Temperature of liquid, \$T=\dfrac{2}{5}\$ distance between lower and upper fixed pointTemperature of liquid, \$T=\dfrac{2}{5}\times 100=40^0C\$On kelvin scale, \$T_k=273.15+40\$ \$T_k=313.15K\$The correct option is B.

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Structure of Laboratory Thermometer

Q: Draw a neat labelled diagram of a laboratory thermometer.

Labeled diagram of of a laboratory thermometer is shown in the figure below:

Q: State four reasons for using mercury as a thermometric liquid.

Reasons for using mercury as a thermometric liquid are :(a) Mercury has uniform contraction and expansion (b) Mercury does not stick to the sides of the capillary tube Thus it helps in recording accurate temperature (c) Mercury is opaque and shining Thus it can be easily seen as a fine thread in the capillary tube(d) It has high boiling point \$ \displaystyle 257^{\circ}C \$ and low freezing point (\$ \displaystyle -39^{\circ}C \$) so it can be used to measured and only wide range of temperatures

Q: Two thermometers are constructed in the same way except that one has a spherical bulb and the other a cylindrical bulb; which one will respond quickly to temperature changes?

\$\textbf{Solution}:\$1. The flow of heat is proportional to the surface area or area of cross-section.2. We know that, the surface area of a cylindrical bulb is more than that of spherical surface. 3. Therefore, the thermometer with cylindrical bulb responds more quickly to temperature change than the thermometer with spherical bulb.\$\textbf{Hece A is the correct option}\$

Q: Four arrangements to measure temperature of ice in beaker with laboratory thermometer are shown in Figure (a. b. c and d).Which one of them shows the correct arrangement for accurate measurement of temperature?

We know that the clinical thermometer should be held straight without any bend and should be kept inside that substance completely so that bulb can take the right measurements so this criterion is satisfied by the fig (a) and (b).But the clinical thermometer should not touch the surface but we see that in fig (b), thermometer touches the bottom surface which is not correct as it leads to faulty measurement value so fig a is the correct choice.

Q: Boojho has three thermometers as shown in above Figure. He wants to measure the temperature of his body and that of boiling water. Which thermometer (s) should he choose?

The image (I) and (III) are the clinical thermometers that are used to measure the body temperature only.The correct answer is option (a). Thermometer (i) or (iii) for measuring body temperature and (ii) for measuring the temperature of boiling water.

Q: Which of the following is not true about Laboratory thermometers ?

A laboratory thermometer is a tool used in laboratories to measure temperature with high accuracy. It can be partially or fully immersed in the substance being measured. A laboratory thermometer is recognizable by its long stem with a silver bulb at the end. The silver color in the bulb normally indicates the presence of mercury. Mercury expands as the temperature increases, thus raising the reading, while decreasing temperatures contract the mercury, lowering the reading. Mercury-in-glass thermometers are less used in the 21st century as preference is shifted to other types of thermometers, such as digital, alcohol-filled and organic-based thermometers.hence,Laboratory thermometers are \$not\$ used to measure body temperature.

Q: Boiling water can be measured by

Laboratory thermometers are used to measure temperatures or temperature changes with a high degree of precision. That's why these are mainly used in laboratories. For exp : To measure boiling points of solutions, water etc. They are made up of glass , the strength of which, is increased through thermal tempering or annealing. Types : liquid-in-glass, bimetallic strip, infrared based thermometer. Hence, the answer is Laboratory thermometer.

Q: At low temperatures ................. type of thermometer is used.

Alcohol thermometer.Reason: Alcohol expands uniformly. It has a low freezing point (\$-115^oC\$) therefore it is very suitable for the place where the temperature gets very low. It is an easily available cheap liquid, which is safe to use.Alcohol is cheaper than mercury, and if you break the thermometer, it is not toxic.

Q: An ideal thermometer should have

A thermometer has to attain the temperature of the body fast. So it should draw as little heat from the body as possible so that the existing temperature of the body is not disturbed appreciably. Therefore, the heat capacity of an ideal thermometer should be as much small as possible.

Physics

definition

Construction and working of types of thermometer

Laboratory thermometers:They are used to measure temperatures or temperaturechangeswithahighdegreeofprecision.Theyaremadeofmetalorglassandstrengthenedthroughprocessessuchasthermaltemperingorannealing.For example, liquid-in-glassthermometersaremadeofsealedglassandcontainafluid,usuallymercuryorredcolouredalcohol,whosevolumechangesrelativelytoitstemperature.Bimetallicstripthermometersincludetwodifferentmetalsthatarebondedtogetherandexpandatdifferentratesastheywarmup.Longbimetallicstripsarewoundintoacoilandusedwithadial.
Clinicalthermometer: It isdesigned forclinicaluse inhumansoranimals.Itismadeofafinecapillarywithabulbfilledwithmercuryatoneend.Nearthebulb,ithasanarrowbendknownasconstriction.Beforeuse,thethermometerisjerkedsothatthemercuryflowsbackintothebulb.

definition

Importance of Laboratory Thermometer

The range of a laboratory thermometer is generally from 10C to 110C. Hence it is not used for measuring body temperature.
Importance of laboratory thermometer:

Laboratory thermometers are designed small to make it potable.
Bulb of laboratory thermometer is usually larger than its bore in order to contain more liquid, to improve its sensitivity.That's why its more precise as even a small change in temperature will make the liquid to rise in the capillary tube.

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