Conduction and Convection

Bell Work Key terms wordsearch

Lesson Objectives Understand in simple terms how the arrangement and movement of particles determine whether a material is a conductor or an insulator Use the idea of particles moving apart to make a fluid less dense Explain simple applications of convection

Present Learning - Conduction experiment Add a blob of wax to one end of the copper and hold the other end in the yellow Bunsen flame. How long does it take for the wax to melt and drop off the metal strip? Now do the same for wood. Why are the times very different?

Conduction in metals Metals are good conductors of heat because: Metals have atoms inside them and lots of free electrons. The free electrons can move around and vibrate. The heat energy is passed on by neighbouring electrons vibrating along the metal.

Conduction – compare a metal and a non-metal If you touch a piece of wood and a piece of copper metal that are both at room temperature (e.g. both at 25°C), which material feels warmer? The wood feels warmer because it is a poor conductor. The wood cannot conduct heat away from your hand as quickly as the copper, which is a good conductor.

Conduction in non-metals Non-metals are poor conductors of heat. In a non-metal, heat energy is only passed on by neighbouring particles vibrating along the non-metal (no free electrons). This allows a flow of energy from hot to cold.

Draw this table into your books Conduction Convection

Present New Information You are going to watch several demos showing conduction and convection. As you are being shown the demos, you need to make notes about each method of heat transfer.

Conduction in liquids 100°C 0°C Metals are good conductors of heat and non-metals are poor conductors of heat (insulators). Are liquids good at conducting heat? Use some gauze to hold an ice cube at the bottom of a tube of water. 100°C Carefully heat the water at the top of the tube only, until this water is boiling. 0°C If the liquid is good at conducting, the ice should quickly melt – it doesn’t. Liquids are poor conductors of heat (i.e. good insulators).

Conduction in gases Liquids are poor conductors of heat (good insulators). Are gases good at conducting heat? Carefully hold a safety match 1 cm away from a Bunsen burner flame. (Do not put the match in the flame!) If a gas is a good conductor, the air between the flame and the match should conduct heat and light the match – it doesn’t. Gases are poor conductors of heat (i.e. good insulators).

Convection and density To understand how heat can be transferred by convection, the idea of density is important. If water, oil and air are mixed up, they will settle out in order of density – which one will rise to the top? The air is least dense and rises to the top, the water is the most dense and sinks to the bottom – it depends on how far apart the particles are.

Convection current in a liquid The movement of hotter areas in a liquid can be seen using potassium permanganate as a dye: This cycle is called a convection current. heat heat Can you explain how the convection current moves using the idea of density?

Convection currents in coal mines When shaft mining was first used to mine coal, convection currents caused by an underground fire were used to ventilate the shafts: Why do you think miners don’t use this method anymore?

Mini Review

Construct Learning . Pierre, a vulnerable penguin, 25 years old, was going bald, which left him with an embarrassingly exposed, pale pink bald patch. Pierre needs his feathers to keep warm, What can we do to keep him warm?

Construct Learning What's black and white and warm all over? A penguin in a wetsuit, naturally. Sounds like a joke, but it's quite serious for biologists at the California Academy of Sciences, who had a wetsuit created for him.

Apply your knowledge Using the knowledge gained from conduction and convection, design Pierre the best wetsuit possible using your science knowledge Success Criteria A clear diagram, describing what materials are used and what properties they have to make them suitable

Apply your knowledge 2 You are asked to go to the arctic for a research expedition. Design using the knowledge gained in today's lesson a outfit to keep you warm

Review – Summary Using your bell work wordsearch write a review of today's lesson using all the key words included. Success Criteria Include all key words Use scientific language Use full sentences

Review Understand in simple terms how the arrangement and movement of particles determine whether a material is a conductor or an insulator (comprehension) Use the idea of particles moving apart to make a fluid less dense (comprehension) Explain simple applications of convection (knowledge)