Thermodynamics Concept Page - 2

Definition

Significance of clinical thermometer to measure body temperatures

The temperature of every person may not be 37C. It could be slightly higher or slightly lower. Actually, what we call normal temperature is the average body temperature of a large number of healthy persons.The clinical thermometer is designed to measure the temperature of human body only. The temperature of human body normally does not go below 350C${35}^{0}C$ or above 42oC${42}^{o}C$. That is the reason that this thermometer has the range 35oC${35}^{o}C$ to 420C${42}^{0}C$.We cannot use clinical thermometer to measure temperature of hot milk as hot milk has more temperature than the range of clinical thermometer.

Definition

Precautions while using clinical thermometer

• Thermometer should be washed be fore and after each use ,preferably with an antiseptic solution.
•  Do not wash the thermometer with hot water.
•  Ensure that before use the mercury level is below 35 ∘C${}^{\circ }C$.
• Read the thermometer keeping the level of mercury along the line of sight.
•  Handle the thermometer with care, as you handle any glass articles.
•  Dont hold the thermometer by the bulb while reading it.

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.

Definition

Describe graduation of a mercury column on Celsius scale

Celsius proposed a method of calibrating a thermometer:
1. Place the cylinder of the thermometer in melting ice made of pure water and mark the point where the fluid in the thermometer stabilises.
2. This point is the freeze/thaw point of water.In the same manner mark the point where the fluid stabilises when the thermometer is placed in boiling water vapour.
3. Divide the length between the two marks into 100 equal parts.

These points are adequate for approximate calibration but both vary with atmospheric pressure. Nowadays, the triple point of water is used instead of the freezing point (the triple point occurs at 273.16 kelvins (K), 0.01 C).

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

Fahrenheit Scale

On the Fahrenheit scale, the freezing point of water is 32 degrees Fahrenheit (F) and the boiling point is 212 F (at standard atmospheric pressure). This puts the boiling and freezing points of water exactly 180 degrees apart.TC=59(F−32)$T_C={\displaystyle \frac{5}{9}}(F-32)$

Definition

Relation between various scales of temperature

Let ,
TK:$T_K:$ Temperature in Kelvin.
TC:$T_C:$ Temperature in degree celsius.
TF:$T_F:$ Temperature in Fahrenheit.
TK=273.15+TC$T_K=273.15+T_C$
TC=59(F−32)$T_C={\displaystyle \frac{5}{9}}(F-32)$

Definition

Internal energy

Internal energy is the inherent microscopic energy of a system associated with the random motion of its molecules. Its SI units is joules.

Definition

Units of heat

Some common units of heat are:

• SI unit: Joule(J$J$)
• CGS unit: 1 J=107 erg$1J={10}^{7}erg$
• Calorie, 1 cal=4.186 J$1cal=4.186J$

Definition

Calorie

The energy needed to increase the temperature of one gram of water from 14.50C${14.5}^{0}C$ to 15.50C${15.5}^{0}C$ at a pressure of 1 atm is a calorie. 1calorie=4.184 joules$1calorie=4.184joules$

Definition

Heat

The energy being transferred between two bodies or between adjacent parts of a body as a result of temperature difference is called heat. Thus, heat is a form of energy.

Definition

Factors affecting the amount of heat flow

Amount of heat transferred depends on:

1. Mass of the body(m).
2. Temperature difference of the body(Δt$\mathrm{\Delta }t$).
3. Nature of the substance.

⟹Q∝mΔt$⟹Q\propto m\mathrm{\Delta }t$
Q=cmΔt$Q=cm\mathrm{\Delta }t$
where, c$c$ is the constant of proportionality(called specific heat capacity). It is dependent on the nature of the body.

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