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Chapter 17

Presented by: Jonathan

Nathan

Owen

Chapter 17

Effect of heat and its Transmission

Chapter 17

Overview

How to answer this Questions?

  • What are some effects and applications of expansion and contraction?

Questions ?

  • How does the particulate nature of matter help us better understand about heat transmission?
  • Why do solids expand the least, followed by liquids and then gases, which expand the most
  • What are some good and poor conductors of heat?
  • What does conduction, convection, radiation mean?

17

How are we suppose to answer these questions correctly?

17

Lets take a look at Chapter 17 first ........

Effects of Heat

When solids are cooled, they contract

When solids are Heated, they expand

Effects of

Heat

Expansion is the process in which an object increases in size because it gain heat.

Contraction is the process in which an object decreases in size because it loses heat

Temperature

Temperature

A thermometer is used to measure temperature

The SI unit for Temperature is Kelvin (K)

Other units of Temperature is Degrees celsius ( °C) and Degrees Fahrenheit ( °F)

Temperature is different and has a fixed starting point called absolute zero, which is defined as Zero Kelvin (0 K) and is equivalent of -273.15 °C (-459.67 °F)

Formula used to convert °C to K :

0 K = -273.15°C

Effect of expansion and contraction

Effects and Problems caused by expansion and contraction and the solution to resolve it.

Problem

Solution

Electrical cables

wires and cables are hung loosely from pole to pole

Telephone wires and electricity cables contract in cold weather. They may snap or break

Water pipes

Water pipes and oil pipe lines can expand on hot day, causing them to burst

Expansion bends are made so that the pipes can bend without any damage

Concrete roads

Cracks appear on the roads because the roads expand during hot weather

Expansion gaps are found every few meters in the concrete path to allow for expansion.

Transmission of heat

Heat Transmission

Conduction

Convection

Radiation

What is this?

Lets explore what is

Conduction

Radiation

Convection

Conduction

Conduction

The transfer of heat from one medium to another medium in contact with it

How it occurs

How it occurs

Conduction occurs when two objects at different temperatures are in contact with one another. Heat flows from the warmer object to the cooler object until they are both at the same temperature. Reaching equilibrum.

Applications to daily life

When cooking, the heat from the pan transfers to the food, therefore cooking your food.

Applications in daily life

how conduction works

When a solid is heated at one end, the particles at the hot end vibrate vigorously. the particles then transfer heat through one another through collisions between neighbouring particles, thus it conducts heat.

Describing how conduction works using particulate nature of matter

Heat can also be conducted from a hotter region to a cooler region in liquids and gases

However liquids and gases are poor conductors of heat unlike solids which is a good conductor of heat

>>>>> Lets find out why solids are generally better conductors of heat than liquid and gas <<<<<

This is because particles in liquids and gases are further apart from one another than those in solids

As a result, this particles collide and vibrate together lesser and transfer of heat to neighbouring particles is slower

Therefore, liquids and gases are poor conductor of heat while solids are good conductor

Some

Types of conductor and insulator of heat

Conductors Insulators

rubber

silver

Good and poor conductor of heat

iron

ceramics

gold

plastic

copper

Fabric

Convection

What is Convection ?

Convection is the transfer of heat through the fluid by the movement of the fluid itself.

Convection

Convection

Why Convection current can only occur in fluids?

  • Gases and liquids are also called fluids
  • The particles in a fluid are able to move freely as they are not in a fixed position and particles are far and further apart from one another compared to those in a solid, thus convection is able to take place in fluids.
  • The particles in a solid are closely packed and held in fixed position and cannot move about freely. Therefore, a convectional current cannot take place in solids.

Convection

How Convection take place

Coloured ice cubes are commonly used to enable us to observe the convection current clearly due to the colour crystal

Convection in liquids

The water near the top of the beaker is cooler than the water at the bottom of the beaker. The water near the top of the beaker contracts, becomes denser and sinks. The water at the bottom of the beaker is hotter, thus it expands, becoming less dense and thus rises. The difference in the movement of the cooler and the hotter water sets up a convection current in the beaker.

Convection

How convection take place

Why is smouldering paper used ?

So that we can observe the convection current through smoke particles produced from smouldering paper.

Convection in Gases

The air near the flame is heated and becomes hotter, the heated air is less dense and thus rises. The air near the smouldering paper is cooler, the cooler air is denser and thus sinks, taking the place of the hot air near the flame. The movement of the hot and cool air sets up a convection current.

Convection

Application of convection current in daily life

  • One example is the air conditioner
  • An air conditioner is installed near the top of the wall to ensure effective cooling of a room.
  • As the air near the top of the wall is being cooled by the air conditioner, the cooled air becomes denser and sinks. The hotter air near the bottom of the room becomes less dense and rises and later it is being cooled and sinks again.
  • The movement of the air forms a convection current. Eventually the room is cooled by convection current

Radiation

-Transfer of heat by radiation takes place at the speed of light and travels great distances

Radiation

Radiation is the transfer of heat energy without the need for a medium in the form of electromagnetic waves

Radiators and absorber of heat

Types of Good and poor radiator and absorber of heat

Feature

Characteristic of good absorber and radiators

Characteristic of good absorbers and radiator

Black, dull

White, shiny

colour of surface

Rough

Smooth

Texture of surface

Temperature

Rate of heat loss

-The rate of heat loss or heat gain by radiation is affected by temperature,the nature of the surface and the total exposed surface area of the object.

-The higher the temperature of an object, the more radiation it emits

-The greater the total surface area exposed ,the greater the rate of heat absorbed or radiated

-The dark duller or rougher the surface, the more heat absorbed or radiated

Application of radiation

Black pipes on the solar water heater

Black pipes are placed on the solar water heater so that they can absorb radiation from the sun quickly to heat up the water

Application

Application of heat transfer

:Vacuum flask:

Application

of heat transfer

Vacuum flask function

Vacuum flask

A hot liquid in a vacuum flask stays hot because the vacuum flask is designed to reduce heat lose from liquid by conduction, convection and radiation. The different parts of the flask work together to keep the liquid hot.

Plastic stopper

  • The mouth of the flask is stoppered using a poor heat conductor. Thus reducing conduction and prevents convection from occuring

Silvered glass walls

  • The glass walls are painted in silver as the silver surface of the silvered glass wall is a poor absorber of heat radiation and reflected radiated heat, thus reduces convection and radiation

Vacuum

  • A vacuum is created between the glass walls by removing air. Thus, conduction and convection cannot take place.

Cork to hold flask

  • the cork help to hold the flask firmly and reduce conduction

Mind map of chapter 17

Chapter 17 mind map

Effect of Heat

Heat

Gases expands the most, followed by liquid then solid, which expand the least

Temperature

Effects

Electric cables are hang loosely to prevent it to snap and break during cold weather

Can be measured using thermometer

Expansion when heated and contraction when cooled

Problems and solution in daily life

Concrete roads have expansion gaps so that it will not crack in hot weather

Absolute zero is the lowest temperature

SI unit of temperature is Kelvin (K)

Water pipes have expansion bends to prevent it from bursting

Transmission of heat

Application :

Spoon stiring a cup of tea

Boiling a cup of water

Transmission of heat

Application :

Black pipes are place on a solar water heater

Conduction

Convection

Radiation

Application :

Air conditioner

Electric kettle

Transfer of heat without the need for the medium itself

The transfer of heat from one medium to another medium in contact with it

The transfer of heat through the fluid by the movement of the fluid itself

Vibration of particles and direct contact between particles

Heated fluid expands, become less dense and rise

Cooled fluids contracts, becomes denser and sinks

  • Rate of radiation is affected by
  • Nature of surface,
  • Surface area of the object,
  • Temperature of object.

Poor conductors like plastic conduct heat slowly

Good conductors like iron and steel conduct heat quickly

Good heat radiator and good heat absorber. black dull and rough surfaces

Poor heat radiator and poor heat absorber. White shiny and smooth surface

Form Convection current

Cause of global warming

The sun keeps the Earth warm through conduction, convection and radiation

Global warming is the rise in the average temperature of the Earth surface

Global warming is caused by natural and man made

Natural

Why global warming?

Man-made

Organism breathe out carbon dioxide and release carbon dioxide when they die or decay

Burning of Fossil fuel in power stations, factories and motor vehicles

There are many other more reasons to it

If you have notice, the answers to the question about Heat and its Transmission can be found in the content.

look at it carefully and remember what you have learn and do apply it !

Chapter 17 mind map

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