Do not forget to give your graph a heading. Remind learners of the activities they did in Matter and Materials, especially linked to conductivity. Here are a list of instructions for your reference: You can ask the learners to draw posters explaining how to light a Bunsen burner as an additional exercise if you feel they need the extra practice and reminders. You can lead the discussion in the following way: This investigation will show the learners that metals conduct heat better than non-metals. It may just be that it is conducting heat faster away from your hand. [4 marks]. Why do you think we can do this? AIM: To investigate which materials are the best conductors of heat. When you remove the cake from the oven, which is more likely to burn you more, the metal cake tin, or the cake? The Lee’s Disc experiment determines an approximate value for the thermal conductivity k of a poor conductor like glass, cardboard, etc. The values obtained will depend on the size of the envelopes the learners make as well as the amount of sunlight to which the envelopes were exposed. Could you also feel warmth from the candle? As an extension exercise you could include another investigation in which you measure the rate of energy conduction along a metal rod. This is one way in which energy is transferred and this is called conduction. Connect the to the gas outlet securely and make sure it won't easily come off if moving the Bunsen burner around. The smoke is drawn down under the cardboard and up next to the candle. Learners must mention the term convection current. Investigation: Which metals are the best conductors of heat? Learners should conclude that black surfaces absorb the most radiation and therefore show the biggest and fastest increase in temperature, whereas shiny surfaces absorb the least, as they reflect the most. This transfer of energy is called radiation. Put a thermometer into each of the envelopes and record the starting temperature. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases.Cutting fluids are made from petroleum distillates, animal fats, plant oils, water and air, or other raw ingredients. But, what about when you hold your hand on the side of the candle? A heater should be placed near the floor. The heat is transferred from where it is hottest to the colder end of the rod. Learners can hypothesise about which metal they think will be the best conductor, for example, the copper rod will be the best conductor. Why? The lighter coloured envelope showed a smaller increase in temperature. Explain why. if possible, use a circular ring to stop the melted water from spilling. One blanket cannot trap as much air and so isn't as warm as two blankets. Your parents have a metal hot water geyser and they are complaining about the amount of energy needed to keep the water hot. The more energy that is absorbed, the more that is transferred to the interior, and the higher the temperature. The loss of heat from the rods could affect the results. A measure of the average kinetic energy of the particles of a substance. HYPOTHESIS: Write a hypothesis for this investigation. The best choice to keep the house as warm as possible on the inside is a dark-coloured paint. Write down the materials in order of how fast they conducted heat from the quickest to the slowest. We will learn more about density next year in Gr 8. Both axes must be labelled and show the units of measurement. Explain why. Invite the learners to feel the cold side of the tub and then feel it a few minutes later. We were able to observe this as the potassium permanganate dissolved in the water and moved with the water particles, and then moved downwards again as the water cooled. However, this is a misconception, and will be demonstrated in the activity that it is in fact the aluminium block which causes the ice cube to melt faster as metals are a better conductors of heat. However, if you pose this question to learners again after doing the following investigation and also after looking at the cake and cake tin example, they might then realise that this is another example of a difference in conductivity. Activity-dependent answer. Normal ceramic cups are good conductors of heat and so the energy from the coffee is transferred quickly through the cup to the surroundings. This is not convection as the air particles do not travel sideways when they warm up from the flame. Only the bottom of the pot touches the stove plate, but all of the water inside the pot, even the water not touching the sides, becomes warmer.
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