Vikasana-Bridge Course 2012 - Karnataka · Introduction Heat may be defined as energy in transit...

HEAT AND TEMPERATURE

Vikasana-Bridge Course 2012

TOPICS TOPICS Introduction

Effects of heat

Specific heat

Basics of thermodynamics Basics of thermodynamics


Introduction Introduction iHeat may be defined as energy in transit

from a high temperature region to a lower temperature region.

To understand Effects of heat such as change of temperature expansions of solids liquids gases temperature , expansions of solids , liquids, gases and change of state it is important to know the nature of heat energy . gy


CONT…We know that matter consists of atoms and molecules. These atoms and molecules are in a state of motion.

The motion can be translational, rotational and vibrational and vibrational.


Cont…The particles of matter posses kinetic energy due to such motions.gy

The attraction and repulsion between the The attraction and repulsion between the particles give rise to potential energy .


Cont…

The sum of the kinetic and potential energies is called internal energy or thermal energy .

The internal energy which can be The internal energy which can be transferred from one body to another is called heat energy or heat .called heat energy or heat .


Cont….The internal energy may be increased by transferring energy to the object from a g gy jhigher temperature object‐ this is properly called heating.g

Heat can be felt in terms of physical Heat can be felt in terms of physical changes like hotness, coldness or change of state of matterstate of matter.


Cont….Heat can cause a change in body’s temperature by changing the internal p y g genergy of the body.

Heat transfer is conduction, convection or radiationradiation.


Cont..


Cont …. Cont …. Heat energy is produced at the expense of mechanical energy and vice versa.gy

Ex: ‐ Rub your palms vigorously, palm becomes warmerbecomes warmer.

H i bl i i i d Heat is measurable quantity it is expressed in calorie or Joule.

1 calorie = 4.2 jouleVikasana-Bridge Course 2012

Cont …. Cont ….

1 calorie = The quantity of heat required to 1 calorie The quantity of heat required to raise the temperature of one gram of water by one degree centigrade.by one degree centigrade.


Cont …Cont …S I unit of heat is Joule

Sources of heat The Sun , hot object Burning fire wood & other fuels Burning fire wood & other fuels


HEAT ENERGY FROM THE SUN


HEAT ENRGY FROM BURNING OF WOOD


TEMPERATURETEMPERATURE

EXPERIMENT:‐Take three pans, one containing hot water the second Luke warm and the third cold. Suppose you place your one h d i h t d th th i ld t f ti Th l hand in hot and the other in cold water for some time. Then place both your hands in lukewarm water you will observe that the hand which was previously in contact with hot water will now feel cold, where as the other feels hotwhere as the other feels hot.

HOT WATER LUKE WARM WATER COLD WATER


Cont …It thus shows that the sensation of degree of hotness is just relative to our bodyhotness is just relative to our body.

So temperature is the property of a body that determines the sensation of hotness or coldness when we touch the body.


ACTIVITIESACTIVITIESActivity 01 : ‐Suppose the two pans, one containing a small and other a large amount containing a small and other a large amount of water are placed over identical gas burners and heated for length of time. The bu e s a d eated o e gt o t e. etemperature of the small amount of water will have risen higher than that of the large a e se g e t a t at o t e a geamount. In this instance the increase in temperature are not equal.p q


ACTIVITIESACTIVITIESActivity 02: ‐ On the other hand suppose the two pans are both initially at 30oC p y 3temperature and that both are to be heated to 60oC. It is evident that more heat to be supplied to the pan containing larger amount of water. The temperature change is p gsame for both the quantities of heat supplied are very different.pp y


Thermal equilibrium Thermal equilibrium

We all know that hot water or milk when left We all know that hot water or milk when left on a table begins to cool gradually. Ultimately, it attains the temperature of the Ultimately, it attains the temperature of the surroundings.


Cont..Cont..Similarly, a glass of ice‐cooled water when left on a table for some time will no longer gremain cold and finally tends to attain the temperature of the surroundings. p g

This shows that when two bodies at different This shows that when two bodies at different temperatures come in contact with each other the hotter body becomes cooler and the colder the hotter body becomes cooler and the colder becomes warmer.


Cont..Finally a state is reached when no heat is flow from one body to other.y

The state when no heat is exchanged The state when no heat is exchanged between the two bodies in contact with each other is known as the state of each other is known as the state of thermal equilibrium.


Cont..At this stage two bodies are said to be at the same temperature.


MEASUREMENT OF TEMPERATURE MEASUREMENT OF TEMPERATURE Measurement of temperature is based on the effect on the change of physical g p yproperty of the matter due to transference of heat. heat.

An instrument based on any of the below thermometric property is called a thermometer.


EXAMPLES EXAMPLES Expansion of solids and liquids Increase of volume/ pressure at constant / ppressure/volume of a gasChange in electrical resistance of a piece of g pmetallic wireSetting up of electromotive force at the g pjunction of two dissimilar metals Change in vapour pressureg p pChange of chemical phase of a system etc.


Types of thermometers Types of thermometers Liquid thermometers:‐ It works on the principal of change in volume of liquid with change in temperature. Range of temperature measured is -30oC g p

to 357oCEx : ‐Mercury in glass thermometer (used Ex : Mercury in glass thermometer (used

widely for measurement of ordinary temperature)temperature)


CONT..CONT..MERCURY THERMOMETER CLINICAL THERMOMETER


Gas thermometers :‐It works on the principal of change in the pressure with change in temperature.Range of temperature measured is -200oC

to 1000oCEx:‐ Constant volume gas thermometer (

used in bureau of standards and some used in bureau of standards and some research laboratories)


CONT …Gas thermometer


Resistance thermometer It works on the principal of change of resistance with change of temperature.Range of temperature measured is -200oC

– 1200oC1200 CEx :‐ Platinum resistance thermometer


Cont..


Thermoelectric thermometerThermoelectric thermometer

It works on the principal of change of h f h hthermo emf with change in temperature.Range of temperature measured is -200oC g p

– 3000oCEx :‐ Cu – Fe thermo couple: Cu e t e o coup e

Sb‐ bi thermo couple


CONT …. CONT …. Thermoelectric thermometer


Radiation pyrometersIt works on the principle of amount of radiation falls .


Bimetallic strip thermometerIt works on the principle of linear expansion of solid with temperature.


Temperature scales A number of temperature scales are in use.

These scales have a lower fixed point (LFP) which is the temperature of pure ice at one which is the temperature of pure ice at one atmosphere pressure.

It is also called ice point.


Temperature scales Also these scales have upper fixed point (UFP) which is the temperature of steam at 1 patmospheric pressure.

It is also called steam point.


Cont…It measures the average Kinetic Energy of a substance. In other words, it measures the ,average motion of the molecules in a substance.

The interval between the ice point and the The interval between the ice point and the steam point is divided into different number of divisions for different scales as shown in the divisions for different scales as shown in the table below.


cont.. cont.. celsius scale • oC

h h i FFahrenheit scale • oF

Kelvin scale • K


Cont.. Cont..


Different types of temperature scalesyp pName of the scale

Symbol for each

Lower fixed point

Upper fixed point

No of divisions

degree on the scale

Rea m r o R 0oR 80oR 80Reaumur o R 0oR 80oR 80

Celsius o C 0oC 100oC 100

Fahrenheit o F 32oF 212oF 180

Rankine Ra 460Ra 672Ra 212


Kelvin K 273 K 373K 100

Relation between the temperature on different scales


The zero of the Kelvin scale is called absolute zero.

The Kelvin scale is often termed as the absolute scale.

In common use the absolute zero In common use, the absolute zero corresponds to ‐273oC .

However its exact value is -273.16oC


Different temperature scales have the same reading at following temperatures

Celsius and Fahrenheit at‐40oC = ‐40oF40 C 40 F

F h h it d K l i t Fahrenheit and Kelvin at 574.25oF = 574.25 K

Fahrenheit and Reaumur at-25.6oF = -25.6oR25.6 F 25.6 R


Different temperature scales have the same reading at following temperatures

Reaumur and Celsius at 0oR = 0oC .

At no temperature the Celsius scale can h h di K l i lhave the same reading Kelvin scale.


QUESTIONS1. Write the differences between heat and temperature ANS : ‐Si no Heat Temperature 1 It is a form of energy It is a measure of degree

of hotness of a bodyof hotness of a body

2 Heat is responsible for temperature

It is one of the effects of heat p

3 It is the sum of energies of all molecules

It is the average kinetic energy of the molecules

4 S I unit is joule S I unit is Kelvin


4 S I unit is joule S I unit is Kelvin

CONT…2. What temperature is the same on Celsius

scale as well as on Fahrenheit scale.Ans : ‐ ‐40 3 Why a thick glass tumbler does break 3. Why a thick glass tumbler does break

when a hot liquid is poured in it?A Th i id f h l d f Ans:‐ The inside of the glass expands faster

because the heat comes to it faster than the id i k d outside so it cracks under pressure.


Cont…4. When can we say that our body is hot ?Ans: ‐ If heat energy flows from any body to Ans: If heat energy flows from any body to our body .

5. When can we say that our body is cold ?y y

Ans; If heat energy flows from our body to any body any body .


Cont…6. When the temperature increases what happens to molecular

vibrations. Ans: ‐ Increases

7. What is the value of volume of a gas at zero gKelvin .Ans: ‐ zero Ans: zero


Cont…8. What is the value of pressure of a gas at zero KelvinAns : ‐ Zero

9 Write the relation between temperature in Kelvin scale and Celsius scaleAns:‐ K = 273 + oC


CONT.. 10) What does the temperature scale on the thermometer measure.Ans: ‐ It measures the average Kinetic Energy of a substance. In other words, it measures the average motion of the molecules in a substance.

11) The Fahrenheit and Kelvin scale agree at a reading of Ans :‐ 574


Cont.. 12) A body A is in thermal equilibrium with the body

B and B is in thermal equilibrium with C Ans: - A and C are in thermal equilibrium

13. Normal body temperature on Fahrenheit scale is 98.6oF what is the same temperature on C l i d K l i l ?Celsius and Kelvin scale?

Ans :- T = 37oCT = 310oK


ALL THE BEST STUDENTS ALL THE BEST STUDENTS


Date post:	29-Jul-2018
Category:	Documents
Upload:	trinhthuy
View:	221 times
Download:	0 times

Vikasana-Bridge Course 2012 - Karnataka · Introduction Heat may be defined as energy in transit...

Documents