How can we insulate homes and other buildings?
Double Glazing Loft Insulation Cavity Walls and cavity wall insulation Carpet with underlay Draught Excluders For each of these explain how they reduce heat transfer. Most insulators work by trapping air. Since air is a poor conductor of heat this reduces the rate of energy transfer. Insulators such as loft insulation (often made from fibre glass) and cavity wall insulation (often made from foam) trap very small pockets of air. This not only creates a poor conductor of heat but it also stops convection currents from taking place. U-values measure the effectiveness of an insulation. The lower the U-value the better the insulation properties. What are the factors that affect rate of energy transfer (e.g. how quickly and object cools):
1. The type of material and object is made from (e.g. metal objects will conduct heat a lot quicker than other materials) 2. The dimensions of the object (small objects have a larger surface area-to-volume ratio compared to large objects - e.g. a mouse cools much quicker than an elephant!) 3. What the object is touching (e.g. if the object is touching a conductor then energy transfer will be high, if it is touching an insulator then energy transfer will be lower) 4. Difference in temperature between object and the surroundings (the larger the difference in temperature between the object and its surroundings then the greater the energy transfer) How are objects designed to increase or decrease heat transfer (e.g. heat sink and vacuum flask) How are some animals adapted to the environmental conditions in which they live Investigating Insulators An insulator reduces the rate of energy transfer Design and carry out an experiment to investigate difference insulators. [Previous Lessons: Kinetic Theory, Conduction – why are solids good conductors? Why is a metal a better conductor than glass, Convection – what is it? Where and why does it occur? Thermal radiation – IR radiation. Which are the best absorbers and emitters of IR. What happens to intensity of thermal radiation with distance?] What is evaporation? The process of a liquid turning into a gas – Demo of hot water bath on a top-pan balance losing mass: What factors increase the rate of evaporation?
Explain the process of evaporation using the kinetic theory (+ draw a diagram) Molecules near the surface that have enough KE can break bonds with neighbouring molecules and escape the liquid to become gas molecules. This means average energy of water left behind decreases and so the temperature of the water left behind decreases. |
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