HEAT AND TEMPERATURE
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TOPICS ¾ Introduction ¾ Effects of heat ¾ Specific heat ¾ Basics of thermodynamics Vikasana-Bridge Course 2012
Introduction ‰Heat may be defined as energy in transit
i
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 . Vikasana-Bridge Course 2012
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. Vikasana-Bridge Course 2012
Cont…
‰The particles of matter posses kinetic gy
energy due to such motions.
‰The attraction and repulsion between the particles give rise to potential energy .
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Cont…
‰The sum of the kinetic and potential energies is called internal energy or thermal energy .
‰The internal energy which can be transferred from one body to another is called heat energy or heat .
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Cont….
‰The internal energy may be increased by g
gy
j
transferring energy to the object from a higher temperature object‐ this is properly g
called heating.
‰Heat can be felt in terms of physical changes like hotness, coldness or change of state of matter.
state of matter
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Cont….
‰Heat can cause a change in body’s p
y
g g
temperature by changing the internal energy of the body. ‰Heat transfer is conduction, convection or radiation.
radiation
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Cont..
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Cont …. ‰Heat energy is produced at the expense of gy
mechanical energy and vice versa.
Ex: ‐ Rub your palms vigorously, palm becomes warmer.
becomes warmer
‰ Heat is measurable quantity it is expressed H i bl i i i d in calorie or Joule.
1 calorie = 4.2 joule
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Cont …. ‰1 calorie 1 calorie = The quantity of heat required to The quantity of heat required to raise the temperature of one gram of water by one degree centigrade.
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Cont …
‰
S I unit of heat is Joule ‰ Sources of heat ¾
¾
The Sun , hot object Burning fire wood & other fuels Vikasana-Bridge Course 2012
HEAT ENERGY FROM THE SUN
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HEAT ENRGY FROM BURNING OF WOOD Vikasana-Bridge Course 2012
TEMPERATURE
¾ 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 hand in hot and the other in cold water for some time. Then place ti
Th l 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 hot.
where as the other feels hot
HOT WATER LUKE WARM WATER COLD WATER
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Cont …
¾It thus shows that the sensation of degree of hotness is just relative to our body.
hotness is just relative to our body
¾So temperature is the property of a body that determines the sensation of hotness or coldness when we touch the body.
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ACTIVITIES
yActivity 01 : ‐Suppose the two pans, one containing a small and other a large amount of water are placed over identical gas bu e s a d eated o e gt o t e. e
burners and heated for length of time. The temperature 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 ge
amount. In this instance the increase in temperature are not equal.
p
q
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ACTIVITIES
y Activity 02: ‐ On the other hand suppose the two pans are both initially at 30
p
y 3 oC temperature and that both are to be heated to 60oC. It is evident that more heat to be supplied to the pan containing larger p
g
amount of water. The temperature change is same for both the quantities of heat supplied are very different.
pp
y
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Thermal equilibrium y We all know that hot water or milk when left on a table begins to cool gradually. Ultimately, it attains the temperature of the surroundings. Vikasana-Bridge Course 2012
Cont..
y Similarly, a glass of ice‐cooled water when g
left on a table for some time will no longer remain cold and finally tends to attain the p
g
temperature of the surroundings. y This shows that when two bodies at different temperatures come in contact with each other the hotter body becomes cooler and the colder becomes warmer.
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Cont..
y Finally a state is reached when no heat is y
flow from one body to other.
y The state when no heat is exchanged between the two bodies in contact with each other is known as the state of thermal equilibrium.
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Cont..
y At this stage two bodies are said to be at the same temperature.
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MEASUREMENT OF TEMPERATURE ™Measurement of temperature is based on g
p y
the effect on the change of physical property of the matter due to transference of heat. ™ An instrument based on any of the below thermometric property is called a thermometer.
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EXAMPLES ¾Expansion of solids and liquids ¾Increase of volume/ pressure at constant /p
pressure/volume of a gas
¾Change in electrical resistance of a piece of g
p
metallic wire
¾Setting up of electromotive force at the g p
junction of two dissimilar metals ¾Change in vapour pressure
g
p
p
¾Change of chemical phase of a system etc.
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Types of thermometers y Liquid thermometers:‐ It works on the principal of change in volume of liquid with change in temperature. oC
Range of temperature measured is -30
g
p
to 357oC
Ex : Mercury in glass thermometer (used Ex : ‐Mercury in glass thermometer (used widely for measurement of ordinary temperature)
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CONT..
y MERCURY THERMOMETER CLINICAL THERMOMETER
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Gas thermometers :‐
y It works on the principal of change in the pressure with change in temperature.
Range of temperature measured is -200oC
to 1000oC
Ex:‐ Constant volume gas thermometer ( used in bureau of standards and some research laboratories)
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CONT …
Gas thermometer
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Resistance thermometer y It works on the principal of change of resistance with change of temperature.
Range of temperature measured is -200oC
– 1200oC
Ex :‐ Platinum resistance thermometer Vikasana-Bridge Course 2012
Cont..
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Thermoelectric thermometer
y It works on the principal of change of thermo emf with change in temperature.
h
f
h h
oC
Range of temperature measured is -200
g
p
– 3000oC
: Cu
Cu – Fe thermo couple
e t e o coup e
Ex :‐
Sb‐ bi thermo couple
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CONT …. Thermoelectric thermometer
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Radiation pyrometers
y It works on the principle of amount of radiation falls .
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Bimetallic strip thermometer
It works on the principle of linear expansion of solid with temperature.
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Temperature scales y
A number of temperature scales are in use. y These scales have a lower fixed point (LFP) which is the temperature of pure ice at one atmosphere pressure.
y It is also called ice point.
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Temperature scales y
Also these scales have upper fixed point p
(UFP) which is the temperature of steam at 1 atmospheric pressure.
y It is also called steam point.
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Cont…
y It measures the average Kinetic Energy of a ,
substance. In other words, it measures the average motion of the molecules in a substance.
y The interval between the ice point and the steam point is divided into different number of divisions for different scales as shown in the table below.
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cont.. celsius scale Fahrenheit h h i scale Kelvin scale oC
•
•
oF
•K
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Cont.. Vikasana-Bridge Course 2012
Different types of temperature scales
yp
p
Name of the scale
Symbol for Lower fixed Upper fixed No of each point
point
divisions degree
on the scale
Rea m r
Reaumur
oR
o 0o R
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
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Relation between the temperature on different scales Vikasana-Bridge Course 2012
The zero of the Kelvin scale is called absolute zero.
y The Kelvin scale is often termed as the absolute scale.
y In common use, the absolute zero In common use the absolute zero corresponds to ‐273oC .
y However its exact value is -273.16oC
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Different temperature scales have the same reading at following temperatures
y Celsius and Fahrenheit at
‐40
40oC C = ‐40
40oF
y Fahrenheit and Kelvin at F h h it d K l i t 574.25oF = 574.25 K
y Fahrenheit and Reaumur at
-25.6
25.6oF = -25.6
25.6oR
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Different temperature scales have the same reading at following temperatures
y
Reaumur and Celsius at 0oR = 0oC .
y At no temperature the Celsius scale can h h have the same reading Kelvin scale.
di K l i l
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QUESTIONS
Write the differences between heat and temperature ANS : ‐
1.
Si no 1
2
3
4
Heat Temperature It is a form of energy It is a measure of degree of hotness of a body
of hotness of a body Heat is responsible for temperature
p
It is the sum of energies of all molecules S I unit is joule
S I unit is joule
It is one of the effects of heat It is the average kinetic energy of the molecules S I unit is Kelvin
S I unit is Kelvin Vikasana-Bridge Course 2012
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.
when a hot liquid is poured in it?
A
Ans:‐
Th i id f h l The inside of the glass expands faster d f
because the heat comes to it faster than the outside so it cracks under pressure.
id i k d Vikasana-Bridge Course 2012
Cont…
4. When can we say that our body is hot ?
Ans: ‐ If heat energy flows from any body to Ans: 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 Vikasana-Bridge Course 2012
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 g
Kelvin .
Ans: ‐ zero Ans: Vikasana-Bridge Course 2012
Cont…
8. What is the value of pressure of a gas at zero Kelvin
Ans : ‐ Zero 9 Write the relation between temperature in Kelvin scale and Celsius scale
Ans:‐ K = 273 + oC Vikasana-Bridge Course 2012
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
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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 and
Celsius
dK
Kelvin
l i scale?
l ?
Ans :- T = 37oC
T = 310oK
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