heat trandform and waves

• conduction 


  Heat travels through SOLIDS by conduction.All metals are good conductors of heat (let heat pass easily). Some metals are better conductors of heat than others (e.g. copper is an excellent heat conductor and iron is a poor heat conductor).
• Non-metals are poor conductors of heat. They are INSULATORS
• conduction experiment

  To make this a fair test;The rods are the same thickness.The pin is placed the same distance from the Bunsen flame.The same amount of Vaseline is used.ResultThe pins fall off all the pins. The order they fall off is;copper, aluminium, brass then iron.Copper is the best heat conductor and iron is the worst conductor.

  
• convection in liquids

  Hot/Warm liquids rise. They are lighter (less dense) than cool liquids.Cold/Cool liquids fall. They are heavier (more dense) than warm liquids.
• the convection tube

  The purple crystal is placed into the water at the top of the tube. This allows us to see how the water moves.The water is heated in the bottom right hand corner.The water at the top of the tube moves to the left, then falls down the tube.This happens because the warm water in the tube beside the Bunsen rises. Warm water is lighter than cool water. This pushes the water at the top of the tube to the left, and down the side tube.The cool water falls because it is heavier than the warm water.

  
• convection in gases

  Hot/Warm gases rise. They are lighter (less dense) than cool liquids.Cold/Cool gases fall. They are heavier (more dense) than warm liquids.In the 'Chimney Experiment' the smoke rises when the 'smoking' paper is placed above the chimney above the candle - this shows that hot air rises.The smoke falls when the 'smoking' paper is placed above the chimney without the candle - this shows that cool air falls.

  
• Convection Current in LiquidsHot water rises and cool water falls causing a convection current to form.

  Convection Current in GasesThe hot air in the room above the radiator rises and the cool air falls. This causes a convection current to form.
• explain convection

  the warm particles gain more kinetic energy and move further apart.the warm water becomes less dense (lighter).its lighter than the cool water. the cool particles contain less kinetic energy and are close together.the cool water is denser(heavier) than the warm water.the cool water falls.
• THERE IS A THIRD PROCESS OF HEAT TRANSFER  - RADIATIONThe heat reaches the cheese by heat radiation  - all objects radiate heat in all directions.
• Heat travels from the Sun to the Earth by heat Radiation

  Heat cannot reach the Earth by conduction - you would need a solid material joining the Sun and the Earth.Heat cannot reach the Earth by convection. Convection requires liquid or gas particles. The space between is a vacuum (it contains no particles) therefore heat cannot travel to Earth by radiation.
• Radiation  and Dark & Shiny Surfaces

  The cork attached to the dark surface moves before the cork on the polished surface. The dark surface is a better ABSORBER of heat than the polished surface. The wax melts and the cork slides down the metal plate.
• Heater

  • Placed an equal distance from all the metal cans
• Metal cans

  • Same size
  • Different surfaces
• Water

  • Equal amounts of cold water poured into the cans
  • Water temperature in the cans is the same
• Heating

  • Heated for the same length of time
• Temperature measurement

  • Recorded at the start of the test and each minute for a total of 15 minutes
• Absorption of heat from most to least

  • Dull Black
  • Shiny Black
  • Dull Metal
  • Shiny Metal
• Dark & Dull surfaces

  Good absorbers of heat
• Shiny & Light surfaces


  Poor absorbers of heat
• Why do runners wrap a silver sheet around themselves after running a marathon?

  The runners have used up most of their energy reserves during the 26 mile run. They need to keep all energy inside their body. The silver surface is a poor emitter of heat. The runner's body loses less energy.
• Why are houses often painted white in hot countries

  The owner wants to keep the house cool. The white surface is a very poor absorber of heat radiation.
• Why are solar cells black?

  The solar cells need to absorb as much light/heat energy as possible. Black surfaces are excellent absorbers of heat.
• Why do astronauts wear white space suits during a 'space walk'?

  When in direct sunlight temperatures can reach over one hundred degrees Celsius. The white space suit helps the astronaut survive. The white surface is a poor absorber of heat radiation.
• Home Insulation

  Insulating your home reduces the amount of heat lost. This will keep your house warmer, take less fuel to heat your home and save you money.The pictures below shows thermal images of the same house before and after insulation is installed. Red/yellow/orange colours show a high rate of heat loss. Blue colours show a slow rate of heat loss. After insulation is installed the house shows less heat loss.
• Double Glazing

  Double Glazing is made from two layers of glass with a layer of air in between. Glass and air are excellent heat insualtors and reduce heat loss through the windows.
• Cavity Wall InsulationThe outside wall of a house is made of two layers of brick. In modern houses a layer of foam insulation was inserted when the house was built. Foam is an excellent insulator because it has lots of air trapped.Older houses do not have insulation in the cavity between the walls. Polystyrene foam or tiny polystyrene balls can be pumped into the cavity to improve insulation.
• Loft InsulationA thick layer of insulation can be laid in the loft to reduce heat loss. The material is made from fibres with lots of trapped air.
• Carpet Reduces heat loss through the floor.
• Hot Water Tank Jacket-Modern 'Immersion Heaters' have a thick foam covering to reduce heat loss. Older 'Immersion Heaters' do not have a cover. A 'jacket' can be added to reduce heat loss. It is cheap to buy and will save you a lot of money quickly. The jacket is made from fibres with lots of trapped air.
• Draft excluders are fitted around windows and doors to prevent heat loss through 'gaps'. They are cheap to fit and quickly save you money.
• Vacuum Flask

  • Uses conduction, convection and radiation to keep a drink hot or cool
• Outer Casing Made from Plastic

  Reduces heat loss by CONDUCTION because plastic is an insulator
• Double Walled Glass Container

  Reduces heat loss by CONDUCTION because glass is an insulator
• Vacuum between the Glass Walls

  Reduces heat loss by CONDUCTION and CONVECTION because a vacuum contains no particles and prevents conduction and convection
• Plastic Stopper

  Reduces heat loss by CONDUCTION and CONVECTION because plastic is an insulator and the stopper is placed at the top of the flask to prevent convection
• Silver coloured glass walls

  • Silver surfaces are POOR EMITTERS and ABSORBERS of heat radiation
• If the flask is filled with a hot liquid

  The silver surface reduces heat radiation being emitted from the flask
• If the flask contains a cold liquid

  The silver surface reduces heat radiation being absorbed into the flask
• waves 


  Waves carry ENERGY from one location to another.Waves are produced by a DISTURBANCE e.g. a stone falling into a pond.Waves transfer energy due to particles in a material VIBRATING e.g. in a water wave the water particles vibrate and pass on the energy. The particles actually remain in the same location and vibrate backwards and forwards.
• Transverse Waves

  The particles in the medium vibrate at right angles (perpendicular) to the direction of motion of the wave.Examples: Water Waves AND all the electromagnetic waves