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Presented by: Jonathan
Nathan
Owen
Chapter 17
Effect of heat and its Transmission
Chapter 17
Overview
How to answer this Questions?
Questions ?
How are we suppose to answer these questions correctly?
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
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
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
The transfer of heat from one medium to another medium in contact with it
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.
When cooking, the heat from the pan transfers to the food, therefore cooking your food.
Applications in daily life
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
However liquids and gases are poor conductors of heat unlike solids which is a good conductor of heat
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
rubber
silver
Good and poor conductor of heat
iron
ceramics
gold
plastic
copper
Fabric
What is Convection ?
Convection is the transfer of heat through the fluid by the movement of the fluid itself.
Convection
Why Convection current can only occur in fluids?
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.
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.
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
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
-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
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
Silvered glass walls
Vacuum
Cork to hold flask
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
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
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
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
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 !