and Thermodynamics

Heat

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“Heat from the sun is the

driving force of life on earth”

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“The science of Heat and is it’s relation

to work is called thermodynamics”

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Electrical energy can

produce or remove

heat based on

principles of

“Thermodynamics”

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Heat from burning

coal produces steam,

which runs Train

locomotive

coal, petrol, wood gives heat during burning (chemical

reaction)

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Hot or cold “Measuring

temperature” !

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hot cold

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summer winter

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How much hot?

Measured by

“temperature”

How much cold?

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hot cold

45O C

15O C

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summer winter

40O C - 10O C

Trichy Srinagar

What will be the temperature?

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How much hot?

Measured by

“temperature”

Celsius- unit

100O C0O C

How much cold?

37O C

Thermometer

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At -100 c Carbon dioxide gas becomes

solid (it is called dry ice)

At what temperature water becomes solid?

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How much hot?

1000O C-100O C 5000O CGold melts Sun’s outer surfaceGas freezes into solid

How much cold?

Measured by

“temperature”

Celsius or Kelvin

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How it is getting heated

“Heat transfer” ?

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Why ice cream is melting?

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Why ice cream is melting?

Solid

Liquid

Vapor (gas)

Low temperature

(ice cream)

High temperature

Room temperature

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How water becomes steam?

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How water becomes steam?

Solid

Liquid

Vapor (air)

Low temperature

High temperature

Phase

changeheating

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Heat transferred

room temperature

Heat flows from

coffee to room air

to reach

equilibrium

Heat flows from room air to

ice cream to reach

equilibrium.

So ice cream melts

why coffee

becomes cold after

some time?

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Heat transferred

room temperature

Heat flow

High Low

to reach thermal equilibrium

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Heat transfer mechanisms

The heat is transferred along the body from one particle (molecule) to another without the movement of the particles themselves. This is called as conduction.

Conduction (occurs generally in solids)

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Metals are high conductivity material

Insulator

(conductivity very less)

conductor

(conductivity very high)

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conductors insulators

Wood

Wool

plastic

metals

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convection (occurs generally in

fluids)

The heat is transferred from hotterportions to colder portions by theactual movement of particles of afluid is called convection.

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Radiation (can occur without any medium)

Thermal radiation is the energy radiated from hot surfaces as electromagnetic waves. It does not require medium for its propagation.

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White colour tankers & white gaps

Absorption of radiant heat by a body When radiant heat falls on a body a part of it is absorbed by it. There is an increase in its temperature due to this absorption.

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If the surface of a body is painted black it absorbs more heat than when it is painted white.

Black roof white roof

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How to heatHow to “cold”

why it is “burning” ?

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Why do we use petrol in aero planes

instead of coal for running jet engines?

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10 Kg of coal

10 Kg of diesel

A train can run

1 Km

A train can run

4 Km

It means that for same amount of mass, It means that for same amount of mass, diesel produces larger heat compared diesel produces larger heat compared to coalto coal

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We say that We say that DieselDiesel has high has high calorificcalorific content compared to content compared to coalcoal

Calorific value of a fuel is the total quantity of heat produced when a unit mass (or volume) of the fuel is burnt completely.

Unit of calorific value is kJ/g

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coal

diesel

High calorific

So in scooters, buses, we need to carry So in scooters, buses, we need to carry less amount of fuel, since the diesel’s less amount of fuel, since the diesel’s calorific value is highcalorific value is high

petrol

wood

LPG

low calorific

High ash

zero ash

(5)

(15)

(45)

(50)

(100)

(KJ/g)

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