KS3 Energy Conduction, Convection and Radiation

Resources…

Y8 2 Heating and Cooling (Lesson resources)

Term	Definition
particle	a minute portion of matter
Internal energy	Random energy from motion of particles
temperature	heat in a substance
Celsius	Temperature scale based on water BP and MP
convection	Energy movement based on density changes
Joule	Unit of energy measurement
conduction	Energy transfer when particles vibrate
Radiation	Energy transfer via Infra Red EM waves
evaporation	Fast particles escape a liquid taking kinetic energy with them
Boiling point	When a substance starts to break apart and become a gas with large spaces between
Melting point	When substance stops having a fixed shape and atoms slide over each other and can move more freely
Kinetic Energy	Movement energy of particles
Internal Energy	The movement and vibration of structures such as solids.

Temperature

Temperature is the result of the average total kinetic energy of particles in matter. (movement)

Heat is transfer of thermal energy; it flows from regions of high temperature to regions of low temperature.

Thermal energy is stored as kinetic energy and, in molecules and solids, and as potential energy in the modes of vibration. We call this “Internal Energy”

A hot sparkler has a high temperature but low thermal energy in comparison…
A warm bath has a lot of thermal energy but a low temperature.

Thermal Energy Stores – Kinetic Theory

Theory: A metal consists of a lattice of atoms, each with a shell of electrons. This is also known as a positive ionic lattice. The outer electrons are free to dissociate from their parent atoms and travel through the lattice, creating a sea of electrons, This sea is a kinetic energy store and freely moves through the metal when there is an external temperature difference.

Conductors and Conduction

The heat passes through the saucepan from the gas flame or electric element by conduction. Conduction is the way that heat is transferred in a solid.

Some solids conduct heat better than others. The best conductors by far are metals. Copper is especially good at conducting heat. Expensive saucepans often have a copper bottom to quickly conduct heat through the base to the food inside.

Many non-metals such as paper, cloth, wood and plastic are bad conductors of heat. We say they are thermal insulators.

Air is also a very bad thermal conductor. Things like duvets and ski jackets keep us warm because they are made from a padded material that traps lots of air between its fibres. This makes it a very good insulator.

We can explain conduction by thinking about what is happening to the particles in a solid.

The particles in a solid are close together and arranged in a regular pattern. They vibrate on the spot.
Heating the solid at one end transfers energy to the particles there and they vibrate more.
They bump into nearby particles, transferring energy to them and making them vibrate more.
These then bump into particles further along.
In this way heat energy is quickly transferred to the other end of the solid.

With the exception of mercury, ALL LIQUIDS ARE POOR HEAT CONDUCTORS.

This is because the particles in liquids are further apart than the particles

in solids. GASES are worse HEAT CONDUCTORS than liquids. They are good HEAT INSULATORS.

This is because The particles in gases are much further apart than they are in liquids.

Heat energy can move through a substance by conduction. Metals are good conductors of heat, but non-metals and gases are usually poor conductors of heat. Heat energy is conducted from the hot end of an object to the cold end.

The electrons in piece of metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now charged metal ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have. This kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons. These move through the structure of the metal, colliding with ions as they go.

Convection

The movement of warm and cool air creates a convection current. Birds, like this soaring bald eagle, use convection currents to rise and fall with very little effort. So do gliders which are aeroplanes without engines. An aeroplane tows a glider up into the sky. When they separate the glider uses convection currents, called thermals, to stay in the air.

A current, called a convection current becomes present in the liquid If thermal energy is supplied. The cooler liquid falls and Warmer, less dense liquid rises. The cycle continues as the heat is supplied. Energy is transferred. The Earth’s lithosphere (the crust) is cracked into a number of large pieces (tectonic plates) which are constantly moving. This is as a result of convection currents within the Earth’s mantle driven by heat released by natural radioactive processes.

In the usual water and dye experiment with a square shaped shaped pipe….

The water near the flame gets hot and expands because the
particles in the hot water move faster and get further apart.
The water becomes less dense and so rises.
Cooler, denser water moves in to take its place.
This water gets heated, and so on.
Soon the coloured dye has spread all around the tube and all the water is heated.

Have you ever wondered why smoke goes up a chimney? The smoke is hot. Hot air, as well as smoke, rises. The rising of warm air through colder air is called convection.

The air particles gain energy, moving faster.
The atoms move further apart so the density is now lower
the less dense air rises.
The colder air contracts and falls as particles lose energy.
Lower density air falls towards the ground

Infrared radiation

All objects give out and take in thermal heat which is also called infrared radiation. The hotter an object is, the more infrared radiation it emits. Infrared radiation is a type of electromagnetic radiation that involves waves NOT particles, so it can travel through a vacuum. Black objects are strong emitters of IR radiation, meaning that they give off large amounts of IR radiation. Silver objects are poor emitters of IR radiation, meaning that they give off small amounts of IR radiation.

Leslie’s cube is a device used in the measurement or demonstration of the variations in thermal radiation emitted from different surfaces at the same temperature.

In use, the cavity was filled with hot water; the entire cube has essentially the same temperature as the water. The IR detector showed much greater emission from the side with varnish than from any of the other three sides. (dull)

Vacuum Flask

A vacuum flask stops heat energy being lost by conduction, convection and radiation. As well as keeping coffee hot it can keep drinks cold.

The vacuum has no particles. It stops heat energy being lost by conduction. It stops heat energy being lost by convection. The vacuum does not stop energy being lost by heat radiation – infrared.

The shiny walls reflect the infrared radiation so it cannot escape. Shiny surfaces are poor emitters and absorbers of heat radiation.

The stopper is made of an insulating material. It stops heat energy being lost by conduction through the shiny silver surfaces. It also stops heat energy being lost by convection.

Evaporation and Condensation

Condensation: The particles in a gas have different energies but if a colder object touches them they may condense to form a liquid. They don’t have enough kinetic energy to remain as separate particles so the coalesce into groups to form a liquid.

Evaporation: Some particles in a liquid will have enough kinetic energy to escape from the liquid and become a gas. The remaining particles in the liquid have a lower average kinetic energy than before, so the liquid cools down as evaporation happens.

The rate of evaporation increases if….

the temperature of the liquid is increased.
the surface area of the liquid is increased.
air is moving over the surface of the liquid.

Liquids Conduct Heat Poorly

This simple idea shows how energy is not conducted well by a fluid. Heat ice and water to see if boil at the top and and still be frozen at ...the bottom.[+] Show More

Liquids Conduct Heat Poorly

This simple idea shows how energy is not conducted well by a fluid. Heat ...

Infrared Radiation

This is a video taken at the NEC in Birmingham at the Grand Designs Live ...

Conduction in a Copper Rod

This is the traditional experiment you do to look at conduction. Try ...

Convection Smoke Chimney Mine

Amazing expansion of air

IR Radiation and Matt black or Silver Absorption

Beyond the red end of the visible range, but at frequencies higher than ...

Beyond the red end of the visible range, but at frequencies higher than those of radar waves and microwaves, is the infrared region of the electromagnetic spectrum. William Herschel, a ...German-born British musician and self-taught astronomer, discovered this form of radiation in 1800 by exploring, with the aid of a thermometer, sunlight dispersed into its colors by a glass prism.

Infrared radiation is absorbed and emitted by the rotations and vibrations of chemically bonded atoms or groups of atoms and thus by many kinds of materials. For instance, window glass that is transparent to visible light absorbs infrared radiation by the vibration of its constituent atoms. Infrared radiation is strongly absorbed by water and by the atmosphere. Although invisible to the eye, infrared radiation can be detected as warmth by the skin. Nearly 50 percent of the Sun's radiant energy is emitted in the infrared region of the electromagnetic spectrum, with the rest primarily in the visible region.

Infrared radiation plays an important role in heat transfer and is integral to the greenhouse effect, influencing the thermal radiation budget of the Earth on a global scale and affecting nearly all biospheric activity. Virtually every object at the Earth's surface emits electromagnetic radiation primarily in the infrared region of the spectrum.

In this video we prove the simple idea that a black object can absorb IR strongly whilst a silver metallic object does not. This is a simple test for use at KS3 to help differentiate between materials. We can liken it to putting your hand on a white painted line on a black tarmac road and seeing that the black tarmac is hotter. Also a white shirt is reflective and a black shirt absorbs more IR in hotter climates.

Dark, matt surfaces are good absorbers and emitters of infrared radiation.

Light, shiny surfaces are poor absorbers and emitters of infrared radiation. An example of this is the silvering inside a vacuum flask.

Uses of infrared radiation.

infrared heaters give out infrared radiation to heat a room

PIR’s (passive infra red devices), these can be found as part of home security alarm systems

thermal imaging cameras, police helicopters use these cameras to help find people when flying at night

the silvering on the inside of a vacuum flask helps prevent heat loss from coffee in the flask[+] Show More

Led replacement bulbs

These are cool new led bulbs which are energy efficient. Advantages of LED ...

These are cool new led bulbs which are energy efficient.

Advantages of LED Bulbs

The operational life of a LED lamp (up to 50,000 hours) is in contrast to the average life ...of an incandescent bulb, which is approximately 1000-2000 hours. For lights in very inaccessible places, using LEDs would eliminate the need for difficult bulb replacement for many years. It really is simply a case of fit-and-forget!

The cost of LED lights compared to traditional incandescent bulbs

The main advantage of LED lighting is clearly in the energy savings (and therefore money savings!) which are achieved. The way in which LEDs achieve this energy saving is by the amount of heat they create. Traditional incandescent bulbs lose up to 90% of their power on creating heat which is wasted. LEDs save on power consumption by generating considerably less wasteful heat.

The cost savings are considerably higher than just the energy saving if you consider the cost of 30-50 replacement incandescent bulbs. With LEDs, there would be no replacement bulbs required for many years and they often pay for themselves in energy savings in less than a year of use.

For commercial premises like retail outlets, hotels and offices, there is a significant maintenance cost in replacing light bulbs which can be virtually eliminated. This is an important point, especially where there are a large number of bulbs in place. Eliminating the constant need to replace bulbs by changing to LED options can be very attractive, and after the cost of replacing halogen bulbs is taken into account, LED bulbs really are the ultimate energy saving bulb.

Compact Size

As the LEDs which provide the light in the bulbs are so small, the high powered LED bulbs are direct replacements for halogen bulbs in terms of size. This gives LEDs a distinct advantage over energy saving CFL bulbs which are generally larger than their halogen counterparts, and can look unsightly in some elegant light fittings.

When it comes to display or accent lighting, the compact size of LED light bulbs, as well as the availability of coloured lighting provides for very versatile lighting which is appropriate everywhere from retail displays to Christmas lights in homes.

Practical Advantages

LED light bulbs represent the safest form of lighting and even when they go wrong, they are still not dangerous to be around, unlike incandescent bulbs which generate lots of heat when in use and have even been known to explode when things go wrong. LEDs are not strictly light bulbs, they are an electrical circuit (semiconductor). They do not contain filaments and therefore are not prone to the usual light bulb problems associated with incandescent bulbs.

LEDs will invariably last 30 to 50 times longer than standard incandescent bulbs, whilst using an average of 90% less power which makes them ideal for places where lights are switched on for lengthy periods of time. More durable with no fragile parts, the bulbs generate virtually no heat and are therefore safe in almost all areas around the home. The cool running temperature of LEDs could reduce air conditioning costs, and the fire risk associated with overheating incandescent bulbs is not an issue with LEDs.

As LEDs are very strong and durable, they are able to endure vibration so they are appropriate for use in many places where existing bulbs are subject to regular failure, eg around heavy machinery. They are also able to tolerate low temperatures and therefore allow more flexibility in their use.

LEDs do not produce any UV (ultraviolet) or IR (infra red) radiation, and can thus be used to light paintings or other precious artefacts without causing any fading. Unlike CFL or fluorescent lighting, LED lighting also does not flicker, and this reduces eye strain and other problems associated with flickering lighting solutions.

Taking Care of the Environment

Taking care of the environment has become a way of life in the 21st century, and we all have a duty to try and reduce our carbon footprints, be it at home or in our businesses. An easy way to make a start in improving the efficiency of our homes and businesses is through LED lighting. Environmental specialists list improving energy efficiency as an important factor to reduce our impact on the environment. LED lights use up to 90% less electricity than standard halogen bulbs and have an extremely long lifespan which equates to considerably reduced carbon emissions and less waste because fewer lamps need to be disposed of.

Have you seen the light yet?[+] Show More