Chemistry_Grade_10-12 (1).pdf

In a wetsuit is able to keep their body temperature

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in a wetsuit is able to keep their body temperature much higher than they would otherwise. Activity :: Investigation : A closer look at thermal conductivity Look at the table below, which shows the thermal conductivity of a number of different materials, and then answer the questions that follow. The higher the number in the second column, the better the material is at conducting heat (i.e. it is a good thermal conductor). Remember that a material that conducts heat efficiently, will also lose heat more quickly than an insulating material. 16
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CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10 1.7 Material Thermal Conductivity (W/m/K) Silver 429 Stainless steel 16 Standard glass 1.05 Concrete 0.9 - 2 Red brick 0.69 Water 0.58 Snow 0.5 - 0.25 Wood 0.04 - 0.12 Polystyrene 0.03 Air 0.024 Use this information to answer the following questions: 1. Name two materials that are good thermal conductors. 2. Name two materials that are good insulators. 3. Explain why: (a) cooler boxes are often made of polystyrene (b) homes that are made from wood need less internal heating during the winter months. (c) igloos (homes made from snow) are so good at maintaining warm temper- atures, even in freezing conditions. Interesting Fact erest Fact It is a known fact that well-insulated buildings need less energy for heating than do buildings that have no insulation. Two building materials that are being used more and more worldwide, are mineral wool and polystyrene . Mineral wool is a good insulator because it holds air still in the matrix of the wool so that heat is not lost. Since air is a poor conductor and a good insulator, this helps to keep energy within the building. Polystyrene is also a good insulator and is able to keep cool things cool and hot things hot! It has the added advantage of being resistant to moisture, mould and mildew. Remember that concepts such as conductivity and insulation are not only relevant in the building, industrial and home environments. Think for example of the layer of blubber or fat that we find in animals. In very cold environments, fat and blubber not only provide protection, but also act as an insulator to help the animal to keep its body temperature at the right level. This is known as thermoregulation . 1.7 Magnetic and Non-magnetic Materials We have now looked at a number of ways in which matter can be grouped, such as into metals, semi-metals and non-metals; electrical conductors and insulators, and thermal conductors and insulators. One way in which we can further group metals, is to divide them into those that are magnetic and those that are non-magnetic. Definition: Magnetism Magnetism is one of the phenomena by which materials exert attractive or repulsive forces on other materials. 17
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1.8 CHAPTER 1. CLASSIFICATION OF MATTER - GRADE 10 A metal is said to be ferromagnetic if it can be magnetised (i.e. made into a magnet). If you hold a magnet very close to a metal object, it may happen that its own electrical field will be induced and the object becomes magnetic. Some metals keep their magnetism for longer than others. Look at iron and steel for example. Iron loses its magnetism quite quickly if it is taken
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