Transcript Document
Double Lesson Conduction and Convection 21/07/2015 Aim: To explain the processes of conduction and convection Starter: • Touch all of the following objects in the lab • Which is the coolest and hottest? • Shirt • Stand • Bunsen Tube • Bunsen Chimney • Bench • Chair Leg Stopwatch Graph Home Heating and Cooling insulator – a material that is hard for heat energy to flow through. conductor – a material that is easy for heat energy to flow through due to its free electrons fluid – a liquid or gas Conduction heat travelling by particles colliding together. Main heat transfer mechanism in solids. Fluids make bad conductors Convection Currents Main heat transfer mechanism in liquids In your own words explain convection currents In your own words explain convection currents In your own words explain convection currents In your own words explain convection currents Radiation Heat energy transfer by Infra Red electromagnetic waves (like visible light) Does not need particles and is thus the only heat transfer mechanism in a vacuum Stopwatch Graph Home Conductors can be compared to see which is the best. The faster the heat travels through the rod the quicker the pins will drop. Rod 1 Rod 2 Wax melts and tells us that the heat has arrived Stopwatch Graph Home What happens when copper and steel are heated Both steel and copper are good conductors. They are both metals and all metals are good conductors. Conduction of heat Steel Copper Stopwatch Graph Home What happens when copper and glass are heated? Glass will conduct heat but it is a non-metal. Non-metals are poor conductors (insulators). Conduction of heat glass Copper Stopwatch Graph Home Conduction Stopwatch Graph Home Particle model for conduction As the solid gets hotter the particles vibrate faster. These extra vibrations are passed along the rod. This is how the heat spreads and we call this CONDUCTION Hot Cold NON-METAL Stopwatch Graph Home Particle model for the best conductors Positive ions pass the energy on by collision Metals also have free electrons METAL The free electrons move through the metal and help conduction. The electrons pass on energy by colliding with the ions (and other electrons) Stopwatch Graph Home Heating and Cooling insulator – a material that is hard for heat energy to flow through. conductor – a material that is easy for heat energy to flow through due to its free electrons fluid – a liquid or gas Conduction heat travelling by particles colliding together. Main heat transfer mechanism in solids. Fluids make bad conductors Convection Currents Main heat transfer mechanism in liquids In your own words explain convection currents In your own words explain convection currents In your own words explain convection currents In your own words explain convection currents Radiation Heat energy transfer by Infra Red electromagnetic waves (like visible light) Does not need particles and is thus the only heat transfer mechanism in a vacuum Stopwatch Graph Home Conduction in Fluids • • • A fluid is a liquid or a gas Fluids do not conduct well Demo Boiling water in your hand Stopwatch Graph Home Demos 2 gas jars with hot water Convection Loop Stopwatch Graph Home Heating a Gas Stopwatch Graph Home Look at this particle model of a liquid How does the particle motion compare with solids? How will heat spread through a liquid? Stopwatch Graph Home • particles become hot • gain kinetic energy • spread out Particles in a small region of water • less dense water rises (floats up) • particles cool down • lose kinetic energy • move closer • more dense water falls (sinks down) Stopwatch Graph Home Convection Stopwatch Graph Home Heating and Cooling insulator – a material that is hard for heat energy to flow through. conductor – a material that is easy for heat energy to flow through due to its free electrons fluid – a liquid or gas Conduction heat travelling by particles colliding together. Main heat transfer mechanism in solids. Fluids make bad conductors Convection Currents Main heat transfer mechanism in fluids In a paragraph or a set a notes explain convection currents Radiation Heat energy transfer by Infra Red electromagnetic waves (like visible light) Does not need particles and is thus the only heat transfer mechanism in a vacuum Stopwatch Graph Home Convection Currents in Kettles Stopwatch Graph Home Tea Bag Demo Remove all the tea leaves Light the top of the bag Stopwatch Graph Home Think how heat will spread in these diagrams Heat Heat Heat Which way will the paddle wheels move? Heat Heat Stopwatch Graph Home Answers Heat Heat clockwise Heat anti-clockwise Heat Heat Stopwatch Graph Home Sea Breeze Stopwatch Graph Home Stopwatch Graph Home Stopwatch Graph Home Stopwatch Graph Home Stopwatch Graph Home Conduction and Convection recap Aim: To explain the processes of conduction and convection Stopwatch Graph Home Radiation and Insulation 21/07/2015 Aim: To explain the processes of radiation To identify the main mechanisms of insulation Starter: How many senses do you have? Can you feel where the sun is with your eyes closed? Stopwatch Graph Home How does heat get to us from the sun? Stopwatch Graph Home Some examples of Infra Red Movie - Walking in Woodland Man in Chair Movie - Firemen Stopwatch Graph Home Heating and Cooling insulator – a material that is hard for heat energy to flow through. conductor – a material that is easy for heat energy to flow through due to its free electrons fluid – a liquid or gas Conduction heat travelling by particles colliding together. Main heat transfer mechanism in solids. Fluids make bad conductors Convection Currents Main heat transfer mechanism in liquids In your own words explain convection currents Radiation Heat energy transfer by Infra Red electromagnetic waves (like visible light) Does not need particles and is thus the only heat transfer mechanism in a vacuum Black matt objects absorb and emit the most infra red radiation Shiny white objects absorb and emit the least infra red radiation Stopwatch Graph Home Mini Practical Wrap a dark piece of foil around one hand and a light one around the other Which hand gets hot first when held near to a Bunsen? Stopwatch Graph Home Investigating thermal absorption Stopwatch Graph Home Investigating thermal emission Stopwatch Graph Home Heating and Cooling insulator – a material that is hard for heat energy to flow through. conductor – a material that is easy for heat energy to flow through due to its free electrons fluid – a liquid or gas Conduction heat travelling by particles colliding together. Main heat transfer mechanism in solids. Fluids make bad conductors Convection Currents Main heat transfer mechanism in liquids In your own words explain convection currents Radiation Heat energy transfer by Infra Red electromagnetic waves (like visible light) Does not need particles and is thus the only heat transfer mechanism in a vacuum Black matt objects absorb and emit the most infra red radiation Shiny white objects absorb and emit the least infra red radiation Stopwatch Graph Home Infrared radiation – true or false? Stopwatch Graph Home Which type of heat transfer? Stopwatch Graph Home Insulation Charlie forgot to take the chicken out of the freezer last night! Will his plan to defrost the chicken in time for lunch work? Stopwatch Graph Home Effective Insulators Think about the following effective insulating materials What do they have in common? Why are they good insulators? Duvet filling Hair Expanded polystyrene Cotton Stopwatch Graph Home Insulation Insulation will slow down heat flow Keep cold things cold and hot things hot Some materials make good insulators (e.g. ceramics) Most insulators are improved by: trapping pockets of air pockets are too small for convection currents air is a bad conductor Stopwatch Graph Home How does a vacuum flask work? How is a vacuum flask able to keep hot drinks hot and cold drinks cold? 2. The plastic (or cork) lid is an insulator and the screw top prevents convection currents escaping from the flask. 1. There is a vacuum between two layers of glass or steel, which prevents heat leaving or entering by conduction. 3. The walls have silvery surfaces, which prevent heat leaving or entering by radiation. Stopwatch Graph Home Movie Stopwatch Graph Home Multiple-choice quiz Stopwatch Graph Home Insulation recap Aims Identify that gases are poor conductors of heat. Investigate the best way to insulate a test tube of hot water. Stopwatch Graph Home Insulating Homes 21/07/2015 Aim To name methods of insulating housing To state what types of heat transfer they prevent To explain how they work Stopwatch Graph Home Anagrams Stopwatch Graph Home Losing Energy We lose energy from the roof, the door, the walls and the windows. In order to reduce electricity bills and pollution, we need to keep energy losses from our homes to a minimum. Stopwatch Graph Home Home Insulation As we go through the next few slides complete the table below Don’t copy the words on the slides, read and summarise Method Heat transfer How? mechanism prevented Curtain Convection Radiation Stopwatch Graph Home Curtains Curtains reduce draughts [convection currents] leaving the house. They are opaque and so don’t allow much radiated heat to pass through them. Stopwatch Graph Home Home Insulation As we go through the next few slides complete the table below Don’t copy the words on the slides, read and summarise Method Heat transfer How? mechanism prevented Curtain Convection Radiation They reduce draughts (convection currents) Opaque so prevent IR travelling out Stopwatch Graph Home Double Glazing A great deal of energy is lost through windows. By adding an extra pane, the trapped air in between acts as an insulator to reduce heat loss by conduction. The insulating effect of the gap can be improved further by sucking all the air out to create a vacuum. Double glazing is expensive and difficult to smash without a special hammer. Stopwatch Graph Home Cavity Wall Insulation Most outside walls have an empty space between the 2 layers of bricks called a cavity. This reduces heat loss by conduction through the bricks. Cavity wall foam insulation is pumped in between the bricks to prevent convection within the cavity. Stopwatch Graph Home Loft Insulation The air heated by central heating is less dense than the cooler air around it and rises. The ceilings get heated and eventually the heat escapes through the roof. Loft insulation contains trapped air which forms an insulating layer between the rooms and the attic. Stopwatch Graph Home Radiators Radiators heat the wall a great deal - this wastes heat energy. Placing shiny silver coated card between the wall and the radiator reduces heat loss by radiation by reflecting it back into the room. Stopwatch Graph Home Draught Excluders Draughts are convection currents. A great deal of heat energy is lost in this way but it is the easiest type to prevent. Draught excluders are hairy or spongy strips which close gaps and prevent the convection currents escaping. Stopwatch Graph Home Insulation and heat transfer Stopwatch Graph Home Insulation and heat loss – true or false? Stopwatch Graph Home Sim Energy We will be going to the computer room to play sim energy The program is in year 10\teachers\physics\sim energy Double click on sim energy.exe Flat Semi-Detatched Detatched Stopwatch Graph Home Movie: Arctic Clothing Stopwatch Graph Home Keeping Warm recap Aim To name methods of insulating housing To state what types of heat transfer they prevent To explain how they work Plenary Whiteboards types, methods and mechanisms Stopwatch Graph Home