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Boardworks High School Science Conduction and Convection

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Presentation on theme: "Boardworks High School Science Conduction and Convection"— Presentation transcript:

1 Boardworks High School Science Conduction and Convection

2 Boardworks High School Science Conduction and Convection
What is conduction? Boardworks High School Science Conduction and Convection How are the particles arranged in a solid, a liquid and a gas? solid liquid gas Particles that are very close together can transfer heat energy as they vibrate. This type of heat transfer is called conduction. Teacher notes The importance of these visual representations of the arrangement of particles in solids, liquids and gases should be stressed. Students could be asked to discuss the limitations of these models, which include: the models are static whereas the particles are actually moving the models are two-dimensional whereas the particles are actually 3D dimensional. Students could also be asked to discuss the good points of the models and why they are useful. Conduction is the method of heat transfer in solids but not liquids and gases. Why? What type of solids are the best conductors?

3 How do nonmetals conduct heat?
Boardworks High School Science Conduction and Convection Teacher notes This animation shows how heat is conducted through a nonmetal on a particle level. While viewing the animation it should be emphasised that this process is relatively slow, which is why conduction in nonmetals is slow compared to conduction in metals.

4 How do metals conduct heat?
Boardworks High School Science Conduction and Convection Metals are good conductors of heat. The outer electrons of metal atoms are not attached to any particular atom. They are free to move between the atoms. When a metal is heated, the free electrons gain kinetic energy. This means that the free electrons move faster and transfer the energy through the metal. This makes heat transfer in metals very efficient. Teacher notes Please note that this diagram is not drawn to scale. It should be stressed to students that an electron is tiny compared to a metal ion, especially the solid nucleus of a metal ion. This means that the electrons are able to pass between the metal ions. Insulators do not have free electrons and so they do not conduct heat as well as metals. heat

5 What happens a fluid is heated?
Boardworks High School Science Conduction and Convection Liquids and gases can both flow and behave in similar ways, so they are called fluids. What happens to the particles in a fluid when it is heated? less dense fluid heat The heated fluid particles gain energy, so they move about more and spread out. The same number of particles now take up more space, so the fluid has become less dense.

6 Boardworks High School Science Conduction and Convection
What is convection? Boardworks High School Science Conduction and Convection Warmer regions of a fluid are less dense than cooler regions of the same fluid. The warmer regions will rise because they are less dense. The cooler regions will sink since they are more dense. This is how heat transfer takes place in fluids. It is called convection. Teacher notes The diagram illustrates how temperature affects the density of particles in a fluid. When using the diagram it should be highlighted that the particles near the top are further apart and the particles near the bottom are closer together. The widely-spaced particles at the top of the diagram represent a warmer region of the fluid. They are floating on top of a cooler region of air (represented by the particles spaced closely together) because the warm region of the fluid is less dense. The dotted boxes have been included to help students visualize the density of the fluid. Students could be asked to count the number of particles in each box to compare the density of the different regions. It should be noted that the density of the regions of the fluid in this diagram have been exaggerated to increase the contrast and make the regions clearer to see. The steady flow between the warm and cool sections of a fluid, such as air or water, is called a convection current.

7 How does convection in a liquid occur?
Boardworks High School Science Conduction and Convection Teacher notes This three-stage animation uses the example of boiling water in an electric kettle to demonstrate how convection occurs in a liquid. While showing the animation it could be highlighted that the hot water floats up through the cold water because the hot water is less dense. The denser cold water falls below the hot water, pushing the hot water up.

8 How does convection in a gas occur?
Boardworks High School Science Conduction and Convection Teacher notes This three-stage animation uses the example of coastal breezes to demonstrate how convection occurs in a a gas. Red arrows are used to represent the movement of warm air and blue arrows are used to represent the movement of cooler air. Suitable prompts include: Stage 1: Why is the hot air rising? Stage 2: What happens to the warmer air as it moves out to the ocean? Stage 3: Why has the convection current changed direction?

9 Why is convection important in fridges?
Boardworks High School Science Conduction and Convection Why is the freezer compartment at the top of a fridge? The freezer compartment is at the top of a fridge because cool air sinks. The freezer cools the air at the top and this cold air cools the food on the way down. It is warmer at the bottom of the fridge. This warmer air rises and so a convection current is set up inside the fridge, which helps to keep the fridge cool.

10 Conduction and convection – summary
Boardworks High School Science Conduction and Convection Teacher notes This completing sentence activity provides the opportunity for some informal assessment of students’ understanding of conduction and convection.


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