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PIC SCIENCES

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1. HEAT

(THERMOMETRY)

1. Heat: It is the sum of total of kinetic and potential energy

of all the molecules in a given substance which always

flows from a body of high temperature to the body of low

temperature till the temperatures equalize.

2. Temperature: Temperature is the degree of hotness or

coldness of a body or Temperature is a quantity that

decides which body is hotter and which is colder. So

temperature decides direction of heat (energy) flow, where as heat is the energy

itself that flow.

“On the basis of the kinetic model of matter, temperature can be defined as the

average of the kinetic energy of all the molecules of a substance.”

3. Thermal equilibrium: When two bodies are placed in thermal contact, heat

energy will be transferred from the „hotter‟ body to the „colder‟ body. This transfer

of heat energy is continued till both bodies attain same degree of hotness (or)

coldness. At this stage, we say that the bodies have achieved „thermal equilibrium‟.

Thus, „State of thermal equilibrium denotes a state of a body where it neither

receives nor gives out heat energy‟.

4. Specific Heat: The amount of heat required to

rising the temperature of unit mass of a material

through 10C or 1 K is called specific heat or specific

heat capacity.

5. Evaporation: “The

process of escaping of

molecules from the

surface of a liquid at

any temperature is

called evaporation.”

It is a natural process.

6. Condensation: When the molecules of water in air,

during their motion, strike the surface of glass

tumbler which is cool; then the molecules of air lose

their kinetic energy which leads to lower the

temperature and they get converted into droplets.

Hence we can conclude that the temperature of the

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water in glass tumbler increases. This process is called „condensation‟. It is

warming process. “Condensation” can also be defined as the phase changes from

gas to liquid that at the surface of a cool body”.

7. Humidity: Some vapor is always present in air. This vapor may come from

evaporation of water from the surfaces of rivers, lakes, ponds and from the drying

of wet clothes, sweat and so on. “The presence of vapor molecules in air is humid.”

“The amount of water vapor present in air is called the humidity of air.”

8. Dew: During winter nights, the atmospheric temperature goes down. The surfaces

of

window-panes, flower, grass etc, become

still colder. The air near them becomes saturates and condensation begins. “The

water droplets condensed on such surface of any

body are known as dew”.

9. Fog: If the temperature falls further, the whole

atmosphere in that region contain maximum amount

of vapor. So the water molecules present in vapor

condense on the dust particles in air and form small

droplets of water. These “droplets keep on

floating in the air and form a thick mist which restricts visibility. This

thick mist is called fog”.

10. Boiling point: “The process in which the liquid phase

changes to gaseous phase at a

constant temperature “. This

temperature is called boiling

point of the liquid.

11. Latent heat of vaporization:

The heat energy is required to

change 1gr of liquid to gas at

constant temperature is called

latent heat of vaporization.

Note: The boiling point of water at constant atmospheric pressure (1atm) is 1000

C or 373K and latent heat of water is 540 cal/g.

12. Melting point: The process in which solid phase changes

to liquid phase at a constant

temperature. This constant

temperature is called melting point.

13. Freezing point: “The process in

which the substance in liquid

phase changes to solid phase by

losing some energy from it is

called freezing.”

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• If two different systems, A and B, (thermal contact) are in thermal equilibrium

with another system C. then the systems A and B are in thermal equilibrium with

each other.

• The average kinetic energy of the molecules is directly proportional to the absolute

temperature.

• The specific heat capacity of a material is the amount of heat required to rise the

temperature of unit mass of the material by or unit. S=Q/m Δt

• The process of escaping of molecules from the surface of a liquid at any temperature

is called evaporation and it is a cooling process.

• Condensation is the reverse process of evaporation.

• Boiling is the process in which the liquid phase changes to gaseous phase at a

constant temperature and constant pressure

1. What would be the final temperature of a mixture of

50g of water at 200C temperature and 50g of water at

400C temperature? (AS1)

Answer: Data given

m1 = 50 g (Mass of water)

m2 = 50 g (Mass of water)

Temperature T1 = 200C, Temperature T2 = 40

0C

According to method of mixtures

Final temperature T = = = = 300C

2. Explain why dogs pant during hot summer days using

the concept of evaporation? (AS1) Answer: We see generally dogs pant during summer days

to reduce their internal temperature. When dogs pant, the

water molecule present on the tongue and in the mouth

gets evaporate by absorbing some heat energy from their

bodies. Consequently dog‟s bodies get cooled.

3. Why do we get dew on the surface of a cold soft drink bottle kept in open air? (AS1)

Answer: Air contains water molecules in the

form of vapor (due to humidity). When the

molecules of water in air, during their motion,

strike the surface of glass bottle (tumbler)

which is cool; then the molecules of water in

air lose their kinetic energy which leads to

lower the temperature and they get converted

(condensation) into droplets. Such droplets on

surface of bottle are seen as dew.

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4. Write the differences between evaporation and boiling? (AS1)

Answer:

S.No. Evaporation Boiling

1. The process of escaping of

molecules from the surface of a

liquid at any temperature is called

evaporation

The process in which the liquid

phase changes to gaseous phase at a

constant temperature

2. Temperature of the system falls

during evaporation.

Temperature of the system (liquid)

remains same during boiling.

3. It is a cooling process It does not cause any cooling.

4. Evaporation is a surface

phenomenon.

Boiling is a bulk phenomenon.

5. Evaporation takes place at all the

temperatures.

Boiling takes place at boiling point

of the given liquid only.

5. Does the surrounding air become warm or cool when vapor phase of H2O

condenses? Explain. (AS1)

Answer: Air contains water molecules in the form of vapor (humidity). When

the molecules of water in air, during their motion, strike the surface of glass

tumbler which is cool; then the molecules of air lose their kinetic energy which

leads to lower the temperature and they get converted (condensation) into droplets.

The energy lost by the water molecule in air will be given to the molecules of

glass tumbler. Hence the average kinetic energy of the glass molecules increases. In

turn the energy is transferred from glass molecules to the water molecules in the glass.

In this way the average kinetic energy of water molecules in the tumbler rises. Hence

we can conclude that the temperature of the water in glass increases. This process

is called „condensation’. It is warming process. “Condensation” can also be defined

as the phase changes from gas to liquid that at the surface of the liquid”.

Let us examine a situation:

You feel warm after you finish your bath under the shower on hot day. In the

bathroom, the number of vapour molecules per unit volume is greater than number of

vapour molecules per unit volume outside the room. When you try to dry yourself

with a towel, the vapour molecules surrounding you condense on your skin and

this condensation makes you feel warm.

6. Answer these. (AS1)

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a) How much energy is transferred when 1gm of boiling water at 1000C

condenses to water at 1000C?

b) How much energy is transferred when 1gm of boiling water at 1000C

Cools to water at 00C?

c) How much energy is transferred when 1gm of water at 00C freezes to

Ice at 00C?

d) How much energy is transferred when 1gm of steam at 1000C turns

to ice 00C?

Answer:

The heat energy is required to change 1gr of liquid to gas at constant temperature

is called latent heat of vaporization.

Consider a liquid of mass „m‟ requires heat energy „Q‟ calories to change

from its state liquid phase to gas phase. Then Latent heat of vaporization is Q/m.

Latent heat of vaporization is denoted by „L‟. L =

CGS unit and SI unit of latent heat of vaporization is cal/gm and J/kg respectively.

The boiling point of water at constant atmospheric pressure (1atm) is 100°C or 373K

and Latent heat of vaporization of water is 540 cal/gm.

a): Both steam and water have same temperature, which is 1000C

Constant temperature - 1000C,

We know that latent heat of vaporization (L), L =

Quantity of heat transferred Q = m L

The latent heat of vaporization (L) of water is 540cal/gm (at373K and 1 atm

pressure)

L = 540 cal/gm, m = 1gm

Q = m L = 1 X 540 = 540 cal

b): Boiling water at 1000C cools to water 0

0C

T1 = 1000C, T2 = 0

0C and m = 1gm

Quantity of heat transferred Q = mS

= 1 X 1 X (100 – 0) (specific heat of water 1cal/gm – 0C)

= 100 cal.

c):1gm mass of water at 00C freezes to ice at 0

0C

The Heat energy required to convert 1gm of solid completely into

liquid at a constant temperature is called Latent heat of fusion.

Consider a solid of mass m which requires heat energy Q to change from

the solid phase to liquid phase. The heat required to change 1gm of solid into

liquid is Q/m.

Latent heat of fusion L = Q/m. The value of Latent heat of fusion of ice is

80cal/gm

Quantity of heat withdrawn (release) during freezing Q = m L

Latent heat of fusion of ice (L), L = = 80 cal/gm.

Q = m L = 1X 80 = 80 cal. (1gm mass of water)

d):1gm of steam at 1000C turns to ice at 0

0C

Conversion of 1000C steam to 100

0C water releases 540cal/gm,

Conversion of 1000C water to 0

0C water releases 100cal/gm

Conversion of 00C water to 0

0C ice releases 80cal/gm

Total Quantity of heat leased during transfer of 1000C steam to 0

0C ice is

Q = 540cal + 100cal + 80cal

= 720 cal.

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7. Explain the procedure of finding specific heat of solid experimentally. (AS1)

Answer: Determination of Specific heat of solid

Aim: To find the specific heat of given solid.

Apparatus: calorimeter, thermometer, stirrer, water, steam heater, wooden box

and lead shots.

Procedure: The mass of the calorimeter along with stirrer is determined by common

balance. One third of the volume of the calorimeter is filled with water and its mass

is measured as.

The calorimeter is placed in the wooden box and temperature is measured using

thermometer. Lead pieces is placed in steam heater they are heated to a

temperature

is quickly transferred in to calorimeter,

with minimum loss of heat. Contents in

the calorimeter are stirred well and then

resultant temperature is noted.

Since there is no loss of heat to

surroundings, we can assume that the

entire heat lost by the solid is transferred

to the calorimeter and water to reach the

final temperature. The mass of the

calorimeter along with contents is

measured as m3.If, and are the specific heats of the calorimeter, solid pieces and water

respectively.

Heat lost by the solid = Heat gain by the calorimeter + Heat gain by the water

(m3- m1 ) SL(T2-T3) = m1 Sc(T3-T1)+(m2-m1) Sw(T3-T1)

Ss =

Here the specific heat of calorimeter is Sc

The specific heat of lead shot is SL

The specific heat of water is SW

Knowing the specific heat capacities of we can calculate the specific heat of the

solid pieces.

8. Covert 200C into Kelvin scale. (AS1)

Answer: The relation between absolute scale of temperature (K) and degree

Celsius (0C).

K = 0C + 273

Data given C = 200C, K = 20 + 273 = 293K

200C is equal to 293K

9. Your friend is asked to differentiate between evaporation and boiling. What

questions could you ask to make him to know the differences between

evaporation and boiling? (AS2)

Answer: The following questions can be asked

Is evaporation a surface phenomenon? Or Bulk phenomenon?

Is boiling a surface phenomenon? Or bulk phenomenon?

Is evaporation takes place at all the temperatures? Or not ?

Is boiling takes place at all the temperatures or not?

Is temperature of liquid increase or decrease in evaporation?

Is temperature of liquid increase or decrease in boiling?

Note: you can ask in any way.

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10. What happens to the water when wet clothes dry? (AS3)

Answer: When wet clothes are exposed to air by spading in large area, it is

possible to absorb heat energy by water molecules present in the wet cloths change

their state there by leaving the clothes on blowing wind. It is evaporation process

as the water changes its state to vapor at any temperature.

11. Equal amounts of water are kept in a cup and in a dish. Which will evaporate

faster? Why? (AS3)

Answer: The phenomenon of evaporation is depends on three factors, they are

surface area and temperature and humidity. So evaporation increase as increase the

surface area of vassal. The water in dish will be evaporated faster than cup.

12. Suggest an experiment to prove that rate of evaporation of liquid depends on

its surface area and vapor already present in surrounding air. (AS3)

Answer: We know that the rate of evaporation depends on three factors. They are

surface area, temperature and humidity.

To prove the rate of evaporation depends on the above factors

Take a few drops of spirit (say 1 ml) in a Petri dish (a shallow glass or plastic

cylindrical dish used in the laboratory) and a 5 ml test tube separately at room

temperature. (Make sure there is

no flame near it). In a short period

of time you will notice that spirit

in the dish disappears where as in

the test tube some spirit left over.

This is due to surface area of

Petri dish is greater than the test

tube. This observation shows that

evaporation increase in increase of surface area.

If any water vapor (humidity) is already present in air of surrounding area

increase the rate of evaporation. Humidity results a rise in temperature in the

surrounding the dish.

13. Place a Pyrex funnel with its mouth-down in a sauce pan with full of water, in

such a way that the stem tube of the funnel is above the water or pointing

upward into air. Rest the edge of the bottom portion of the funnel on a nail or

on a coin so that water can get under it. Place the pan on a stove and heat it

till it begins to boil. Where do the bubbles form first? Why? Can you explain

how a geyser works using above experience? (AS4)

Answer: Bubbling formation starts from the

bottom of the sauce pan water where nail or

coin arranged here boiling point of water

increase with increase in pressure which is

due to pressure exerted by water column at

that point. So boiling begins near the bottom,

bubbles rise and push out the water as an

eruption. In the same way the geyser works.

The boiling point of deep water rises above

1000C due to pressure exerted by weight of

water column at that point with which water can be pushed out as an eruption.

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14. Collect the information about working of geyser and prepare a report. (AS4)

Answer: Geyser is a source to erupt hot water from underground periodically.

It is a narrow, vertical cavity formed in

the earth crust through which ground

water seeps. This deeper water column

heated and starts boiling above 1000C

due to pressure exerted by the water

column exist up to that point and due to

heat source such as volcano‟s nearby .

The deeper water at this point

considerably hotter than surface water

and conventional transfer of heat is

blocked by narrowness of the geyser.

Therefore it begins boiling near the bottom and the bubbles rising above push the

water out starting the eruption which makes the water rushes out consequently the

pressure on the remaining water is reduced thus boiling process is accelerated

continuously to erupt (spray) hot water into air.

15. How do you appreciate the role of the higher specific heat of water in

stabilizing atmospheric temperature during winter and summer seasons?

(AS6)

Answer: The sun is a bountiful source of energy to radiate onto the earth daily.

This heat energy is absorbed by the water in oceans, seas, and other water sources.

If there is no water, all the heat energy received by the earth‟s atmosphere leads to

a lot of increase in temperature of the earth. But it is not happening due to the

presence of water. As the specific heat of water is high, all the heat energy sent by

the sun is received by water and causes the stabilization of temperature in the

atmosphere. In this aspect we can appreciate the role of higher specific heat of

water in the stabilization of atmospheric temperature.

16. Suppose that 1l of water is heated for a certain time to rise and its

temperature by 20C. If 2l of water is heated for the same time, by how much

will its temperature rises? (AS7)

Answer: Data given

m1 = 1l,S1 = 1 cal/g .0C, = 2

0C m2 = 2l, S2 = 1 cal/g .

0C, = ?

If same quantity of heat is supplied for same time.

Q1 = Q2 = m1 S1 = m2 S2

= = 10C

The temperature raised during this process is 10C

17. What role does specific heat capacity play in a watermelon to keep it cool for

long time after removing it from a fridge on a hot day? (AS7)

Answer: We know that a watermelon contains large extent of water. As the

specific heat of water is very high, it takes more time to increase its temperature of

1gm water by 10C as well as (in reverse), it takes long time to decrease its

temperature to 10C. So watermelon takes a lot of time for cooling when compared

to other fruits in the fridge.

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18. If you are chilly outside the shower stall, why do you feel warm after the bath

if you stay in bathroom? (AS7)

Answer: You feel warm after you finish your bath under the shower on hot day. In

the bathroom, the number of vapour molecules per unit volume is greater than number

of vapour molecules per unit volume outside the room. When you try to dry

yourself with a towel, the vapour molecules surrounding you condense on your

skin and this condensation makes you feel warm.

19. Assume that heat is being supplied continuously to the ice at -50C. You know

that ice melts at 00C and boils at 100

0C.

Continue the heating till it starts boiling.

Note the temperature for every minute.

Draw a graph between temperature and

heat using the values you get. What do

you understand from the graph? Write

the conclusions. (AS5)

Answer:

From the graph given aside we conclude

that

From A to B i.e., (0 to t1) in this zone the

temperature of ice increases. Here

heat given to ice is considered as

specific heat.

From B to C i.e., (t1 to t3) in this

zone ice melts to water at 00C. So

heat is given to ice is considered as

latent heat of fusion.

From C to D i.e., (t3 to t4) in this

zone the temperature of water

increases from 00C to 100

0C. So

heat is given to water is considered

as specific heat.

From D to E i.e., (t4 to t6) in this

zone water converts into steam at

1000C. So heat is given is

considered as latent heat of vaporization.

ACTIVITY: 1

How can you understand the meanings of „coldness‟,

„hotness‟ and „temperature‟ by an activity?

Material required: A piece of wood, a piece of metal, a

refrigerator.

Procedure: Take a piece of wood and a piece of metal and

keep them in a fridge or ice box. After 15 minutes, take

them out and ask your friend to touch them.

When we keep materials in a fridge, they become

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cold i.e., they lose heat energy. The iron and wooden pieces were kept in the fridge for

the same period of time but, we feel that the metal piece colder than the wooden piece.

When you touch the metal or wooden piece, you

feel that they are cold. This means that heat energy is

being transferred from your finger to the pieces. When

you remove your finger, you don‟t get a feeling of

„coldness‟. This means that when heat energy flows out

of your body you get the feeling of „coldness‟ and when

heat energy enters your body you get a feeling of „hotness‟.

You can test this by bringing your finger near the flame of a

matchstick!

So, if you feel that the metal piece „colder‟ than

the wooden piece, it must mean that more heat energy flows out of your body when you

touch the metal piece as compared to the wooden piece. In other words, the „degree of

coldness‟ of the metal piece is greater than that of the wooden piece.

Conclusion: The conventional definition of temperature is “the degree of hotness or

coldness”. We say that the metal piece is at a lower „temperature‟ as compared to the

wooden piece when they are taken out of the fridge.

ACTIVITY: 2

How can you explain the thermal equilibrium with an activity?

Heat: Take two cups and filled one of them with hot water and another with cold water.

Now take a laboratory thermometer, observe the mercury level in it and note it in your note

book. Keep it in hot water. Observe changes in mercury level. Note the reading.

We know that bodies in contact achieve thermal equilibrium due to transfer of heat

energy. When you kept thermometer in hot water you will observe that there is raise in

mercury level. This happens because heat has transferred from hotter body (hot water)

to cold body (mercury in thermometer). Similarly in the second case you will observe

that mercury level comes down from its level because of the transfer of heat from mercury

(hotter body) to water (colder body). Thus we define heat as follows:

“Heat is a form of energy in transist that is transferred from body at higher

temperature to body at lower temperature.”

The steadiness of the mercury column of the thermometer indicates that flow of

heat, between the thermometer liquid (mercury) and water, has stopped thermal

equilibrium has been attained between the water and thermometer liquid (mercury). The

thermometer reading at thermal equilibrium state gives the “temperature”. Thus

„temperature‟ is a measure of thermal equilibrium. If two different systems, A and B in

thermal contact, are in thermal equilibrium individually with another system C (thermal

contact with A and B). We know that if A is in thermal equilibrium with C, they both have the

same temperature. Similarly, B and C have the same temperature. Thus A and B will have

the same temperature and would therefore be in thermal equilibrium with each other.

(A, B and C are in thermal contact).

The SI unit of heat is Joule (J) and CGS unit is calorie (cal).The amount of heat

required to increase the temperature of 1gram of water by 10C is called calorie.

1cal = 4.186 joules

The SI unit of temperature is Kelvin (K). It can also be expressed as degree

Celsius (0C). 0

0C = 273K

Temperature in Kelvin =273+Temperature in Celsius

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Add 273 to the value of temperature in degree Celsius to get the temperature in the

Kelvin scale.

Note: Temperature measured in Kelvin scale is called absolute temperature.

ACTIVITY: 3

Explain that the average kinetic energy of the molecules is directly proportional to

the absolute temperature by activity.

Take two bowls one with hot water

and second with cold water. Gently

sprinkle food color on the surface of the

water in both bowls .Observe the

motion of the small grains of food color.

You will notice that the grains of

food color jiggle (move randomly). This

happens because the molecules of the

water in both bowls are in random

motion. We observe that the jiggling of

the grains of food color in hot water is

more when compared to the jiggling in

cold water. We know that bodies

possess kinetic energy when they are in the motion.

As the speed of motion particles (grain of food) in the water of both bowls is

different, we can say that they have different kinetic energies. Thus we conclude that the

average kinetic energy of molecules / particles of the hotter body are larger than that of a

colder body. So we can say that the temperature of a body is an indicator of the average

kinetic energy of molecule of that body.

“The average kinetic energy of the molecules is directly proportional to the absolute

temperature”

ACTIVITY: 4

Explain an activity to show that temperature determines

direction of heat flow.

Take water in a jar and heat it to 60°C. Take a cylindrical

transparent glass jar and fill half of it with the hot water. Very

gently pour coconut oil over the surface of the water. (Take care

that the water and oil do not mix). Put a lid with two holes on

the top of the glass jar. Take two thermometers and insert them

through holes of the lid in such a way that bulb of the one

thermometer lies inside the water and other lies inside the

coconut oil as shown in the figure 1.

Now observe the readings of the two thermometers. The

reading of the thermometer kept in water decreases, while, at the

same time, the reading of the thermometer kept in oil increases.

Because the average kinetic energy of the molecules of oil increases, while the

average kinetic energy of the molecules of water decreases. In other words, the

temperature of oil increases while the temperature of water decreases.

From the above discussion it is clear that, water loses energy while oil gains

energy; because of the temperature difference between the water and oil. Thus some heat

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energy flows from water to oil. This means, the kinetic energy of the molecules of the

water decreases while the kinetic energy of the molecules of oil increases.

Heat is the energy that is transferred from hotter to colder body. Temperature is a

quantity that decides which body is hotter and which is colder. So temperature decides

direction of heat (energy) flow, whereas heat is the energy itself that flow.

ACTIVITY: 5

Explain that the rate of rise in temperature depends on the nature of the substance

by an activity.

SPECIFIC HEAT: Take a large jar with water

and heat it up to 100o.Take two identical boiling

test tubes with single-holed corks and fill them, one

with 50gm of water and the other with 50gm of oil.

Insert two thermometers through holes of the corks,

one each in two test tubes. Now clamp them to a

retort stand and place them in the jar of hot water

as shown in the figure 2.

Observe the readings of thermometers every

three minutes .Note the readings in your notebook.

We believe that the same amount of heat is

supplied to water and oil because they kept in the

water of same temperature for the same interval of

time.

We observe that the rise in temperature of the oil is faster than the rise in

temperature of the water.

We conclude that the rise in temperature depends on the nature of the material.

ACTIVITY: 6

Explain on what factors the amount of heat observed by a material depends by an

activity.

Take 250 ml of water in one beaker (a small beaker) and 1 litre of water in

another beaker (a large beaker), and note down their initial temperature using a

thermometer (initial temperatures of them should be equal). Now heat both beakers till their

temperature of water in two beakers rises by 90 0C from their initial temperatures. Note down

the heating times required to rise temperature of water by 90 0C in each beaker.

You will notice that you need more time to rise temperature by 90 0C for water in

larger beaker when compared to water in small beaker that means you need to supply more

heat energy for water in larger beaker than water in small beaker for same change in

temperature.

For same change in temperature the amount of heat absorbed by a body is directly

proportional to its mass (m), i.e. Q ∞ m (when ΔT is constant) …………… (1)

Now take 1 liter of water in a beaker and heat it. Note the temperature changes (ΔT)

for every two minutes.

You will notice that the change in temperature rise with time, that means, for the

same mass (m) of water the change in temperature is proportional to amount of heat (Q)

absorbed by it. Q ∞ΔT (when „m‟ is constant) …………………. (2)

From equation (1) and (2), we get Q ∞mΔT (as Q = mSΔT )

Where „S‟ is a constant for a given material. This constant is called “Specific heat” of

substance. S =

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The specific heat of a material is the amount of heat required to rise the

temperature of unit mass of the material by a unit.

CGS unit of specific is cal / g - and SI unit of it is J / kg - K

1 cal/g-0C = 1 kcal /kg-K = 4.2 x J/kg-K = 4.2 KJ/kg-K (Here K=10

3)

ACTIVITY: 7

Explain the principle of method of mixtures by an activity.

PRINCIPLE OF METHOD OF MIXTURES:

When two bodies or more bodies at different temperatures are brought into thermal

contact, then net heat is lost by the hot bodies is equal to net heat gain by the cold bodies

until they attain thermal equilibrium. (If heat is not lost by any other process)

Net heat lost= Net heat gain

This is known as principle of method of mixtures.

Take 100 ml (m1) of water at 900C and 200 ml (m2) of water at 60

0C and mix the two.

Let the initial temperatures of the samples of masses m1 and m2 be T1 and T2 (the

higher of the two temperatures is called T1, the lower is called T2). Let T be the final

temperature of the mixture.

The temperature of the mixture is lower than the temperature of the hotter sample,

but higher than the temperature of the colder sample. This means that the hot sample has

lost heat, and the cold sample has gained heat.

The amount of heat lost by the hotter sample Q1 is m1S (T1- T).

The amount of heat gained by the cooler sample, Q2, is m2S (T - T2).

Since heat lost by the first sample is equal to the heat gained by the other sample

i.e. Q1 = Q2,

Which can be written as m1S (T1 - T) = m2S(T - T2)

Which can be simplified to have the Final temperature T =

ACTIVITY: 8

Explain an activity to determine specific heat of a solid

Aim: To find the specific heat of given solid.

Apparatus: calorimeter, thermometer, stirrer, water, steam heater, wooden box and lead

shots.

Procedure: The mass of the calorimeter along with stirrer is determined by common balance

(m1). One third of the volume of the calorimeter

is filled with water and its mass is measured as

(m2) total mass of water taken is (m2- m1) The

calorimeter is placed in the wooden box and

temperature is measured using thermometer as

(T1) Lead pieces is placed in steam heater they

are heated to a temperature T2 is quickly

transferred in to calorimeter, with minimum

loss of heat. Contents in the calorimeter are stirred

well and then resultant temperature T3 is noted.

Since there is no loss of heat to surroundings, we

can assume that the entire heat lost by the solid is

transferred to the calorimeter and water to reach the final temperature. The mass of the

calorimeter along with contents (lead shots) is measured as m3.If SC, SL and SW are the

specific heats of the calorimeter, solid pieces and water respectively.

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Heat lost by the solid = Heat gain by the calorimeter + Heat gain by the water

(m3- m1 ) SL(T2-T3) = m1 Sc(T3-T1)+(m2-m1) Sw(T3-T1)

Ss =

Knowing the specific heat capacities of SC and SW we can calculate the

specific heat of the lead shots.

ACTIVITY: 9

Write an activity to show that the evaporation increases with increase in speed

Take a few drops of spirit (say 1 ml) in two Petri dishes (a shallow glass or plastic

cylindrical lidded dish used in the laboratory) separately. Keep the one of the dishes

containing spirit under a ceiling fan and switch on the fan. Keep another dish with its lid

closed. Observe the quantity of spirit in both dishes after 5 minutes.

You will notice that spirit in the dish that kept under the ceiling fan disappear. Where as

you will find some spirit left in the dish that kept in lidded dish.

“The process of escaping of molecules from the surface of a liquid at any temperature is

called evaporation”

Let us see the reason for faster evaporation of spirit under the fan. If air is blown over the

liquid surface in an open pan the number of returning molecules is reduced to a large

extent. This is because any molecule escaping from the surface is blown away from the

vicinity of the liquid. This increases the rate of evaporation. This is the reason for the

spirit in Petri dish that kept under ceiling fan evaporates quickly when compared to that kept

in lidded dish. You will notice clothes dry faster when a wind is blowing.

Rate of evaporation of a liquid depends on its surface area, temperature and amount of vapour

already present in the surrounding air.

ACTIVITY: 10

Conduct an activity to show the process of condensation.

Place a glass tumbler on the table. Pour cold water up to half its height. We know that the

temperature of surrounding air is higher than the temperature of the cold water. Air

contains water molecules in the form of vapour. When the molecules of water in air,

during their motion, strike the surface of glass tumbler which is cool; then the

molecules of air lose their kinetic energy which leads to lower the temperature and they

get converted into droplets. The energy lost by the water molecule in air will be given to

the molecules of glass tumbler. Hence the average kinetic energy of the glass molecules

increases. In turn the energy is transferred from glass molecules to the water molecules in the

glass. In this way the average kinetic energy of water molecules in the tumbler rises. Hence we

can conclude that the temperature of the water in glass increases. This process is called

„condensation’. It is warming process.

Let us examine a situation:

You feel warm after you finish your bath under the shower on hot day. In the bathroom, the

number of vapour molecules per unit volume is greater than number of vapour molecules per

unit volume outside the room. When you try to dry yourself with a towel, the vapour

molecules surrounding you condense on your skin and this condensation makes you feel

warm.

ACTIVITY:11

Explain melting with an activity.

Take small ice cubes in a beaker. Insert the thermometer into ice cubes in the beaker.Observe

the reading of thermometer. Now start heating the beaker keeping on a burner. Observe

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changes in the reading of thermometer for every 1 minute till the ice completely melts and

gets converted into water. You will observe that the temperature at beginning is below 0 0C

and it goes on changing till it reaches 00C. When ice starts melting, you will notice that

no change in temperature though you are supplying heat continuously. The heat

energy supplied to the ice increases the internal energy of the molecules of the ice. This

increase in internal energy of molecules weakens the bonds as well as breaks the bonds

between the molecules (H2O) in the ice. That is why the ice (in solid phase) becomes

water (in liquid phase).This process takes place at a constant temperature 0°C or 273K.

This temperature is called melting point. This process of converting solid into a liquid is

called“Melting”.

Consider a solid of mass m which requires heat energy Q to change from the solid

phase to liquid phase. The heat required to change 1gm of solid into liquid is Q/m.

Latent heat of fusion L = Q/m. The value of Latent heat of fusion of ice is 80cal/gm

ACTIVITY:12

Explain boiling with an activity.

Take a beaker of water keep it on the burner .Note the readings of thermometer every 2

minutes

You will notice that, the temperature of the water

rises continuously, till it reaches 100°C. At100°C

no further rise of temperature of water is seen. At

100 0C, though supply heat continues we can

observe a lot of bubbling at the surface of water at

this 100°C temperature. This is what we call

boiling of water “The process in which the liquid

phase changes to gaseous phase at a constant

temperature “. This temperature is called boiling point of the liquid. Note that

evaporation takes place at any temperature, while boiling occurs at a definite

temperature called the boiling point. When boiling process starts, the temperature of the

liquid cannot be raised, no matter how long we continue to heat it. The temperature

remains at the boiling point until all of the liquid has boiled away.

The heat energy is required to change 1gr of liquid to gas at constant temperature is

called latent heat of vaporization.

Consider a liquid of mass „m‟ requires heat energy „Q‟ calories to change from its state

liquid phase to gas phase. Then Latent heat of vaporization is Q/m. Latent heat of

vaporization is denoted by „L‟. CGS unit and SI unit of latent heat of vaporization is cal/gm

and J/kg respectively.

The boiling point of water at constant atmospheric pressure (1atm) is 100°C or 373K and

Latent heat of vaporization of water is 540 cal/gm.

ACTIVITY: 13

Explain expansion of water on freezing by

activity.

Take small glass bottle with a tight lid .Fill it with

water completely without any gaps and fix the lid

tightly in such a way that water should not come

out of it. Put the bottle into the deep freezer for a few

hours. Take it out from the fridge and you will

observe the glass bottle break.

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We know that the volume of the water poured into the glass

bottle is equal to the volume of the bottle. When the water freezes to

ice, the bottle is broken .This means that the volume of the ice

should be greater than the volume of the water filled in bottle. In

short, we say that water „expands‟ (increases in volume) on freezing!

Thus the density of ice is less than that of water and this explains

why ice floats on water.

WATER EXPANSION EXPERIMENT

NATURAL CONSEQUENCES OF ANOMALOUS EXPANSION OF WATER:

1. Water pipe lines often burst in cold countries or on the high hill stations in winter,

because water freezes at sub zero temperature and in doing so expands. Since there

is no space within the pipes for expanding ice, it exerts tremendous pressure and

bursts open the steel pipes.

It is for same reason that people in cold countries leave their taps dropping at night

so as to provide sufficient space for expansion of freezing water.

2. Vegetables, fruits and plants get damaged in severe cold because the water present

in the plant cells on freezing expands and bursts open the cell wall.

3. Frost bite is basically caused for the same reason, because the water in the cells of

human beings (especially in the exposed parts) freezes and in doing so burst open

the cells.

4. In cold countries, as the temperature of air falls below 00C, the water bodies ( like

ponds, rivers and sea) freezes from the top to form ice, whereas the water below

stays at 40C.

Thus, fish and other aquatic life can easily survive in frozen water bodies, as water

below stays at 40C.

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APPLICATIONS OF SPECIFIC HEAT CAPACITY:

1. The sun delivers a large amount of energy to the Earth daily. The water masses

on Earth, particularly the oceans, absorb this energy for maintaining a relatively constant

temperature. The oceans behave like heat “store houses” for the earth. They can absorb large

amounts of heat at the equator without much rise in temperature due to high specific heat

capacity of water.. Therefore, oceans moderate the surrounding temperature near the

equator. Ocean water transports the heat away from the equator to areas closer to the north

and south poles. This transported heat helps moderate the climates in parts of the Earth that

are far from the equator.

2. Water melon brought out from the refrigerator retains its coolness for a longer time than

any other fruit because it contains large percentage of water. (Water has greater specific

heat).

3. The samosa seems to be cool but it is hot when we eat it because the curry inside

samosa contains ingredients with higher specific heats.

1. The SI unit of specific heat is_____________

2. _____________ flows from a body at higher temperature to a body at lower

temperature.

3. _____________ is a cooling process.

4. An object „A‟ at 10 0C and another object „B‟ at 10K are kept in contact, then heat will

flow from _________ to ___________.

5. The latent heat of fusion of ice is _____________.

6. Temperature of a body is directly proportional to _____________.

7. According to the principle of method of mixtures, the net heat lost by the hot bodies is equal

to _____________ by the cold bodies.

8. The suffocation in summer days is due to _____________.

9. ____________ is used as a coolant.

10. Ice floats on water because _____________.

1. Which of the following is a warming process [ ]

a) Evaporation b) condensation c) boiling d) all the above

2. Melting is a process in which solid phase changes to [ ]

a) liquid phase b) liquid phase at constant temperature

c) gaseous phase d) any phase

3. Three bodies A, B and C are in thermal equilibrium. The temperature of B is 450C. Then

thetemperature of C is ___________ [ ]

a) 450C b) 500C c) 400C d) any temperature

4. The temperature of a steel rod is 330K. Its temperature in 0C is ________ [ ]

a) 550C b) 570C c) 590C d) 530C

5. Specific heat S = [ ]

a) Q/Δt b) QΔt c) Q/mΔt d) mΔt/Q

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6. Boiling point of water at normal atmospheric pressure is _________ [ ]

a) 00C b) 100

0C c) 110

0C d) -5

0C

7. When ice melts, its temperature [ ]

a) remains constant b) increases c) decreaes d) cannot say

1. J/Kg.K 2. Heat 3. Evaporation 4. A, B 5. 180

cal/gm

6. Average kinetic Energy. 7. Heat Gained. 8. Humidity. 9. Water.

10. Density of ice is less than that of water.

1. B 2.A 3.A 4.B 5.C 6.B 7.A

ADDITIONAL INFORMATION:

RELATION BETWEEN CELCIUS AND FAHRENHEIT SCALES:

As the length between the two standard points is same, we can say that 100 degrees

Celsius (C) is equal to 180 degrees Fahrenheit (F – 32).

C: (F – 32) = 100: 180 or

100

C =

180

32F or

5

C =

9

32F

Note: The above relation is very useful for converting temperatures from one scale to another.

1. The markings are from 950F to 110

0F on Fahrenheit scale for clinical purpose, because of

human body does not fall below 950F or rise above 110

0F, as in either case death occurs.

2. Normal temperature is nearly 98.40F

3. The markings are from 350C to 43

0C on Celsius scale for clinical purpose.

4. Normal temperature is nearly 370C on Celsius scale.

Note: High boiling point of mercury is (3570C) and low melting point is (-39

0C)

KELVIN SCALE (ABSOLUTE SCALE) OF TEMPERATURE OR SI SCALE OF

TEMPERATURE:

1. We have already defined temperature as the average kinetic energy of the molecules of a

substance. From this, it implies that if the molecules cease to have any kinetic energy,

then the temperature of substance should be zero in absolute terms.

2. This lowest limit of temperature is called absolute zero by Lord Kelvin.

3. This absolute zero is also called as zero Kelvin or Kelvin zero

Kelvin zero (Zero Kelvin): the lowest temperature at which the molecular movement of matter

ceases is called Kelvin zero or zero Kelvin. Its magnitude on Celsius scale is -2730C.

Temp in Kelvin = 273 + tem in 0C

( T ) K = 273 + (t) in 0C

1K (rise or fall) = 10C (rise or fall)

CALORIMETRY:

Calorimetry is a branch of physics which deals with the measurement of heat energy is

called calorimetry.

CGS Unit of heat energy is calorie

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Calorie: The quantity of heat energy required to raise the temperature of 1g of pure water

through 10C is called one calorie. It is too small unit thus a bigger unit was coined and is called

kilocalorie.

Kilocalorie: The quantity of heat energy required to raise the temperature of one kg of pure

water through 10C is called one kilocalorie.

1 kilocalorie = 1000 calories.

Kilocalorie is some times called Big calorie or Doctor‟s calorie or Calorie (with capital C)

SI Unit of heat energy is Joule

1calorie = 4.186J = 4.2 J (approx)

1kilocalorie = 4186 J = 4200J (approx).

HEAT CAPACITY OR THERMAL CAPACITY (C‟):

The amount of heat energy required to raise the temperature of a given mass of a

substance through 10C is called heat capacity or thermal capacity of that substance.

Heat required to raise the temp of given mass of substance through ө0C = H (J)

10C =

H, ( 1

0C = 1K)

SPECIFIC HEAT CAPACITY:

The amount of heat energy required to raise the temperature of unit mass of a substance

through 10C or 1K is called specific heat capacity

In CGS system unit of specific heat capacity is or cal g-1o

C-1

.

In SI system unit of energy of specific heat capacity

is or J kg-1

K-1

.

1cal g-10

C-1

= 4.2 J g-1

0C

-1

1kcal g-1 0

C-1

= 4200 J kg-1 0

C-1

PRINCIPLE OF CALORIMETRY:

It based on the law of conservation energy

which states “The energy in a system can neither be

created nor can it be destroyed and the sum total of

energy is a constant quantity”.

If no heat is lost to surroundings, then

“Heat energy given out by hot body

= Heat energy absorbed by cold body”

i.e., m1 c1 (ө1- ө) = m2 c2 (ө- ө2) (Here ө1 , and ө are temperatures.)

EVERY DAY USE OF HIGH SPECIFIC HEAT CAPACITY OF WATER:

1. Fomentation is heating the swollen parts of body at a moderate temp of about 500C, as it

brings a lot of relief. We use hot water bottle for fomentation purpose, because water can

store in it large amount of heat energy at a fairly low tem, owing to its high specific heat

capacity.

2. Water is used as coolant in the car radiators, as it can absorb large amount of heat energy

from the engine of a car, but it does not rise to very high temperature. It is for the same

reason that the water is used as coolant in thermal power stations, etc.

3. In a way, all animal and plant life, is possible only due to the high specific heat capacity

of water. This is one of the reasons that all living beings have from 70% to 90% water in

their bodies, which in turn helps in regulating their body temperature.

4. When the weather forecast is frost, the wise farmer always waters his fields in the

evening. It is because water has highest specific heat capacity. Thus every 1g of water

liberates 4.2J of heat energy, when its temp falls by 10C.Thus cooling water liberates

large amount of heat energy, which does not allow the temp of the field to fall below 00C.

Hence the crops are saved from the ill effects of the frost.

CHANGE OF STATE:

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Change of state takes place, when the heat energy is supplied to a solid its temp raises, till

a stage comes when it starts melting. Similarly, when the heat energy is supplied to a liquid its

temperature rises, till a stage comes, when it starts (boiling) changing into its vapors.

Melting or Fusion: The constant temperature at which, a solid changes its state into liquid. This

phenomenon is called meting or fusion. And the constant temperature is called melting point or

fusion point.

Freezing point or Solidification point: The constant temperature at which a liquid changes its

state into solid state is called freezing or solidification. And the constant temperature is called

freezing point or solidification point.

Note: Numerical value of melting point and solidification point is same.

e.g., if the melting point of ice is 00C, then freezing point of water is also 0

0C

Boiling or Vaporization: The constant temperature at which a liquid changes its state into its

vapor. This phenomenon is called boiling or vaporization. And the constant temperature is

called boiling point or ebullition point.

Liquefaction: The constant temperature at which a gas changes its state into its liquid state is

called liquefaction. And the constant temperature is called liquefaction point.

Note: Numerical value of boiling point and the liquefaction point is same.

e.g., if boiling point of water is 1000C, then liquefaction point of steam is also 100

0C.

LATENT HEAT OF FUSION: The heat energy supplied to the solid so as to change it into the

liquid state, without any rise in temperature is called latent heat of fusion.

SPECIFIC LATENT HEAT OF FUSION: Amount of heat energy required to melt one

kilogram of solid (one gram of solid in CGS system) at its melting point, without rise in

temperature is called specific latent heat of fusion.

In SI system, Ice has the highest specific latent heat of fusion. Its value is 336000Jkg-1

.

e.g., if 1 kg of ice on melting requires, 336000 J of heat energy, then 1 kg of water at 00C will

liberate 336000 J of heat energy before changing to ice at 00C.

In CGS system, Ice has the specific latent heat of fusion. Its value is 336Jkg-1

.

In old system, Ice has the specific latent heat of fusion. Its value is 80 cal g-1

.

EXPRESSION FOR LATENT HEAT OF FUSION OF SOLID:

Consider a solid, having specific latent heat of fusion „L‟ J kg-1

.

Let „m‟ be the mass of solid.

Thus, heat absorbed or given out during fusion or solidification Q = mL Joules.

SPECIFIC LATENT HEAT OF VAPOURISATION: All the heat energy supplied is utilized

in increasing intermolecular spaces and is stored in the molecules of vapor in the form of

potential energy. This stored energy by the molecules of a vapor is called latent heat capacity.

“It is the amount of heat energy required to change unit mass of a liquid at its boiling

point into its gaseous state without any rise in temperature”.

Its unit in SI system is J/kg or J kg-1

.

Its unit in CGS system is J/g or J g-1

.

SPECIFIC LATENT HEAT OF VAPOURISATION OF STEAM: It is the amount of heat

energy required to change unit mass, say 1kg or 1g of water at 1000C into steam at 100

0C.

Its value is 2260J/g in CGS system or 226X104J/kg in SI system or 540cal/g in old system.

ADVENTAGES OF HIGH SPECIFIC LATENT HEAT OF VAPOURISATION:

1. It is on account of this high specific latent heat of vaporization of water that water from

the soil does not evaporate quickly by the heat of sun, thus, plants are protected from

wilting in excessive heat.

2. As enormous amount of heat energy is required to vaporize one kg of water, therefore,

water from various water bodies evaporate slowly. Thus there is controlled evaporation

and hence condensation. In other words, the rainfall all over the world is fairly regulated,

which is conducive for plants and animal life.

3. The thermal stations use steam as a medium for converting the heat energy of coal to

electric energy, because every gram of steam can carry 2260J of hest energy.

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4. Burns caused by the steam (scalding) are far more severe than those caused by boiling

water. It is because. Every gram of steam at 1000 C contains 2260J of heat energy more

than water at 1000C. It is this excessive energy which causes sever scalding.

Numerical problems on thermometry:

1. Convert 550C into (i) Kelvin (ii) Fahrenheit scales. (328K, 131

0F)

2. Convert 3570C into (i) Kelvin (ii) Fahrenheit scales. (3K, -454

0F)

3. Convert 1080F into (i) Celsius (ii) Fahrenheit scale. (42.22

0C, 315.22K)

4. Convert 1100F into (i) Celsius (ii) Kelvin scale (43.33

0C, 316.33K)

5. Convert 198K into (i) Celsius (ii) Fahrenheit scale. (-750C, -103

0F)

6. When will the numerical value of Fahrenheit thermometer be equal and opposite to value

on Celsius scale? (11.430F or -11.43

0C)

7. When will the numerical value of Celsius and Fahrenheit will be the same? (-400C and -

400F)

Numerical problems on calorimetry:

1. A liquid of mass 0.2 kg and temperature 1350C is cooled to 25

0C. if the specific heat

capacity of liquid is 750Jkg-1 0

C-1

, find the heat energy given out. (16500J)

2. 0.50kg of lead at 3270C is cooled to 27

0C, when it gives off 22500 calories of energy.

Calculate specific heat capacity of lead in (i) calories (ii) joules. (150 cal/kg/0C,

630J/kg/0C)

3. An electric immersion heater is switched on for 8 minutes. The heat supplied by it raises

the temperature of 500g of water from 100C to 60

0C. Calculate the power of heater in

watts. (218.75W)

4. A heater, rated 1000W, is used to heat 1.5kg of water at 400C to its boiling point.

Calculate the time in which the water comes to boil. Sp heat capacity of water is

4200J/kg/0C (378 s)

5. The heat capacity of a solid of mass 175g is 315 J/0C. Calculate sp heat capacity solid.

(1.8 J/g/0C)

6. A copper calorimeter contains 50g of water at 16 0C. When 40 g water at 36

0C is added,

the resulting temperature of mixture is 240C. Calculate the heat capacity of the

calorimeter. (42J/0C)

7. A liquid P of sp. Heat capacity 1800J/kg /K and at 800C is mixed with liquid R of sp.

Heat capacity 1200J/kg/K and at 300C. After mixing, the temp of mixture is 50

0C. In

what proportion by weight are the liquids mixed? (P:R = 4:9)

8. A burner supplies heat energy at a rate of 434J/s for 60s when 40 g of ice at 0 0C changes

to water at 750C. Calculate latent heat of ice. (336J/g)

9. A metal ball of 0.20kg and at 2000C, when placed on an ice block melts 100 g of ice,

when its temp stops falling. if sp. Latent heat of ice is 340J/g. calculate sp. Heat capacity

of metal ball. (0.85J/g/0C)

10. It takes 4.5 minutes for an electric kettle to heat certain quantity of water from 0 0C to its

boiling point. It takes 24minutes to turn all the water at 100 0C into steam. Calculate the

latent heat of vapoursation of steam. (2240J/g)

God bless you all

If any mistake or necessary correction is required, please inform to me.

-Your guide and well wisher

BABU PRASAD MOSUGANTI M.Sc., B.Ed., M.A Lit. (PHYSICAL SCIENCE)

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