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Beat the heat. Just feel the effects of heat. By Bergin.G. Based on 10 th standard Tamilnadu State Board Syllabus . Contents. Learning objectives. Students understand, Transfer of Heat Energy. Specific heat capacity. Principle of the method of mixtures.

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slide1

Beat the heat

Just feel the effects of heat

By

Bergin.G

Based on 10th standard Tamilnadu State Board Syllabus

slide3
Learning objectives
  • Students understand,
  • Transfer of Heat Energy.
  • Specific heat capacity.
  • Principle of the method of mixtures.
  • The issues involved in Thermal expansion.
  • Effect of cooling in evaporation.
  • The principle and working of refrigerator.
  • The concept of latent heat.

home

slide4
The Transfer of Heat Energy

EXIT

  • If heat is removed, temperature of the water will decrease and the heat is transferred to the surrounding until both are at the same temperature. That is around 32o C

When water is heated its temperature rises.

Let us assume that its temperature be around 80oC and surrounding temperature is around 32oC.

EXIT

Click to view principle, and types of heat transfer

slide5
Conduction

What is conduction ?

  • Conduction is the transfer of energy through matter from particle to particle. It can occur in solids.

Every atom is physically bonded to its neighbours in some way. If heat energy is supplied to one part of a solid, the atoms vibrate faster.

As they vibrate more, the bonds between atoms are shaken more. This passes vibrations on to the next atom, and so on. Eventually the energy spreads throughout the solid. The overall temperature has increased.

EXIT

Click to view what is conduction

slide6
Conduction

Fun to do

Direction of heat transfer

Click on the below steps

Clamp a brass rod as shown in the figure

Attach some iron nails to the rod with the help of wax.

Heat one end of the rod using a burner.

What do you observe ?

Discuss with your teacher.

slide7
Good and bad conductors

THINK QUEST -1

THINK QUEST -2

THINK QUEST -3

THINK QUEST -4

Handles of cooking vessels and kettles are made of wood or plastic. Why?

Cooking vessels are made up of metals. Why?

Why we use woolen clothes in winter ?

Copper tubes are used in automobile radiators ?

Click here to get the hint

Click here to get the hint

Click here to get the hint

Click here to get the hint

wood or plastics are

bad conductors

Metals are good conductors of heat.

Copper readily absorbs and conduct away heat from the hot water coming from the engine.

The pores in the woolen clothes filled with air which is a bad conductor..

EXIT

EXIT

EXIT

EXIT

THINK QUEST - 5

Why ice boxes are double – walled conductors?

Click here to get the hint

Air in between the double wall is a bad conductor.

EXIT

slide8
Convection in fluids

What is convection?

Convection is the mode of transfer of heat in fluids where the molecules actually move from one part of the fluid to the other.

EXIT

Convection in air

Convection in water

Click to view what is convection

slide10
Convection in fluids

FACT FILE

As molecules in solids are tightly packed actual moment of molecules is not possible in solids. Hence convection is not possible in solids.

THINK QUEST -1

THINK QUEST -2

Why ventilators are constructed in a room ?

Why chimneys are fitted in the factories ?

EXIT

Click here to get the hint

EXIT

Click here to get the hint

EXIT

To maintain fresh flow of air by convection current.

The hot air took the smoke and poisonous gas from the factory and moves up.

Do you Know?

EXIT

Click to view fact file , Do you know

slide11
Radiation

I feel very hot

EXIT

Water man in front of a campfire feel hotness. Do you think this heat energy is by conduction or convection?. No, heat requires no medium to reach him from campfire. This mode of transfer of heat is called radiation

Click to view what is radiation?

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Radiation

Some time heat energy is forcefully made to flow from a region of lower temperature to a region of higher temperature. To do this we need to supply energy to the system from outside. This outside source of energy is electrical energy. This concept is used in air conditioners and refrigerators.

Let us imagine you are on the top of the earth

I am throwing ozone particles to minimize radiation

I want to minimize heat radiation reaching to earth surface.

FACT FILE

EXIT

Click to view the fact file

home

slide13
Specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of the substance through 1o C.

Specific heat capacity

Fun to do

Click on the given steps

Take 1 kg of water in a beaker

Measure the temperature

Water – 1kg

Heat the water till the temperature

raises through 1o C

The amount of heat required to raise the temperature of the 1 kg of water through 1o c is called specific heat capacity of water

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Specific heat capacity

Water – 1kg

Coconut oil – 1kg

Take equal mass of water and coconut oil. Note their initial temperatures. Using the same burner heat the two beakers for five minutes. Observe that the rise in temperature is different for different liquids. The rise in temperature for two liquids are different. Why? Discus your observation with your teacher.

slide15
Specific heat capacity

FACT FILE

Amount of heat energy absorbed

Among the liquids, the specific heat capacity is maximum for water and minimum for mercury. Hence water is used as a coolant in radiators of automobile engines and mercury is used as a thermometric liquid.

THINK QUEST

When a substance is heated the amount of heat energy absorbed (Q) by the substance is directly proportional to

Mass of the substance (m)

Specific heat capacity which is constant for a particular substance (s)

Change in temperature (T)

Q = m X s X T

Why does a piece of water melon stay cool for a longer time than sandwiches when both are taken out from refrigerator on a hot day ?

EXIT

Click to view fact file

home

slide16
Heat lost or gained by method of mixtures

Click on the given steps

Take some water in a beaker.

Let m1 be mass of water and

s1 be specific heat capacity of water.

water

m1 – mass

S1 - specific heat capacity

Take a metal ball.

Let m2 be mass of metal ball and

s2 be specific heat capacity of the metal

Measure the temperature of water as t1.

  • Metal ball
  • m2 – mass S2- specific heat capacity
  • Metal ball
  • m2 – mass S2- specific heat capacity

water

m1 – mass

S1 - specific heat capacity

water

m1 – mass

S1 - specific heat capacity

Heat the metal ball.

  • Metal ball
  • m2 – mass S2- specific heat capacity
  • Metal ball
  • m2 – mass S2- specific heat capacity

Metal ball

m2 – mass S2- specific heat capacity

Now temperature be t2

Put the ball inside the water.

Heat lost by the ball = m1 s1(t1 – t2)

Heat gained by the water = m2 s2(t2 –t1)

Heat lost by the ball = Heat gained by the water

m1 s1(t1 – t2 ) = m2 s2(t2 – t1 )

home

slide17
Heat lost or gained by method of mixtures

Amount of heat energy absorbed

When two substances at different temperatures are mixed, heat flows from hot substance to cold substance, till both attain the same temperature. Provided no heat is received from or given to the surroundings and also if there is no chemical action in the mixture.

When ice is mixed with water , ice absorb heat from water.

When heated metal ball is put in a cold water , water absorb heat from the hot metal ball.

Amount of heat gained by the ice

= amount of heat lost by water

Amount of heat gained by the water

= amount of heat lost by metal ball

Using principle of mixture we can measure the specific heat capacity of the solids.

slide18
Thermal Expansion
  • Three types of thermal expansion
  • Linear expansion.
  • Superficial expansion.
  • Volume expansion.

Thermal expansion - video

Thermal expansion :

The expansion of a substance on heating is called thermal expansion.

slide19
Thermal Expansion

Linear expansion

Increase in length due to heating is called linear expansion.

Change in length =

∆x

x

superficial expansion

Increase in area due to heating is called superficial expansion.

Change in area = =

∆ y

∆ x

∆ A

∆ X

∆ Y

x

∆x

slide20
Thermal Expansion

Volume expansion

Increase in volume due to heating is called volume expansion.

Initial volume = V

Final Volume = V +

Change in volume =

∆V

∆V

Examples

Linear expansion

Volume expansion (video)

Superficial expansion

home

slide21
Change of state

Matter exists in three states

1. solid

2. liquid and 3. gas.

slide22
Change of state

Melting

Freezing

Vapourisation.

The process in which a solid changes into liquid on heating is called melting.

The change of a liquid into a solid on cooling is known as freezing.

The process in which a liquid changes into vapour on heating is called vapourisation.

example

EXIT

example

example

EXIT

EXIT

Ice changes into water

Water changes into ice

Water changes into steam

Do you Know?

Some materials may change directly from

a solid to a gas. This is called sublimation.

Example : Naphthalene,  CO2 (dry ice)

EXIT

Click to view Do you know?

slide23
Change of state

Heat energy taken from the environment

Sublimation

MELTING

Evaporation

Freezing

Condensation

Deposition

Heat energy released to the environment

home

slide24
Latent heat

If water is heated its temperature rises till it reaches 100oC.If water is heated more than 100o Cits temperature remains constant for some time.

During this time it changes its phase from liquids to gas.

If ice is heated its temperature rises till it reaches 0oC. If ice is heated more than 0o C its temperature remains constant for some time.

During this time it changes its phase from Solid to liquid.

The latent heat of a substance is defined as the amount of heat absorbed by a unit mass of the substance to change its state without

Change of temperature.

home

slide25
Cooling due to evaporation

FACT FILE

On a rainy day, wet clothes take longer time to dry, because large amount of vapour already present in the air, slows down the evaporation.

I feel too cool

Dogs keep their tongue usually out in

summer. Water evaporates from the

tongue and keeps it cool.

EXIT

Water comes out of the pores of the vessel and evaporates. Therefore water remains cool in an earthen vessel by evaporation.

Click to view the fact file

home

slide26
Working principle of refrigerator

When a liquid evaporates it takes in heat energy and cools its surroundings.

When the gas condenses back to a liquid, the latent heat is released.

This principle is used to take heat from inside a fridge, and release it outside.

By compressing gases, we make them hotter.

Letting them expand, we make them cooler.

slide27
Working principle of refrigerator

Evaporator coil

(heat exchange pipe)

Condenser coil

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Expansion

valve

(heat exchange

pipe)

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Compressor

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home

slide28
Latent heat

Latent heat of vapourisationof a liquid is the amount of heat required to convert unit mass of a liquid at its normal boiling point into vapour at the same temperature.

The latent heat of fusion of a substance is the quantity of heat required to convert unit mass of the solid at its melting point to the liquid state at the same temperture.

slide29
Phase transition graph

Time Vs Temperature graph

F

150

100

50

0

-50

Temperature ( o C)

D

E

Time

B

C

A to B - pure iceB to C - a mixture of water and ice all at 0 ºCC to D - pure waterD to E - a mixture of water and steam all at 100 ºCE to F - pure steam

A

home

slide30
Self evaluation
  • 1. Transfer of heat in fluids is due to
    • Conduction b) Convection
  • 2. When a liquid evaporates, its temperature
  • a) rises b)falls C) does not change
  • 3. The process of changing a solid into gas directly is called
  • a) melting b) freezing C) sublimation
  • 4. Evaporation occurs at
  • a) the surface of the liquid b) the bottom of the liquid
  • c) the middle of the liquid d) both at surface and bottom of a liquid
  • 5. When water solidifies to ice
  • a) heat is absorbed b) heat is released
  • b) temperature increases d) ) temperature decreases
  • 6. The volatile liquid used in refrigerator is
  • a) Freon b) water
  • c) helium d) acetone
  • 7. Total amount of heat required to melt the solid is
  • a) H = m s T b) m s c) T s d) L T
slide31
Self evaluation
  • 1. Mercury is used as a thermometric liquid. Why ?
  • 2. Define specific heat capacity of a substance.
  • 3. Define heat capacity of a substance.
  • 4. Why gaps are left in bridges, railway lines and concrete highways ?
slide32

PRESENTED BY

BERGIN .G

MEDIA DOCUMENTATION OFFICER

SHARVA SHIKSHA ABHIYAN

KANYAKUMARI DISTRICT

TAMIL NADU

EMAIL : berging76@gmail.com

Please visit

http://berging76.edu.glogster.com/

http://scienceoftheday.blogspot.com/

http://bergin-digitalclassroom.blogspot.com/

THANK YOU

Background voice by

M.A.Adarshana

EXCEL central school,Thiruvattar

R.Ashick Rajah

EXCEL central school,Thiruvattar