# Metals are good conductors of heat

## Understand physics 3, textbook

13 Our life in a warm bath Warmth is in good hands - the thermos bottle (Fig. 13.1) E1 Fill the thermos bottle with water heated to 40 ° C and close it. Measure the temperature with a thermometer after 30 minutes. The inside of a thermos bottle consists of a double-walled glass vessel. The mirroring inside the glass vessel throws back the heat radiation (reflects it). The outer plastic cover is also a poor conductor of heat and also protects against glass breakage on the inside. The air from the inner space between the two vessel walls is sucked out during manufacture. In this vacuum there can be no heat conduction because there are no particles that can pass the shocks on. 3. What is the thermal conductivity of substances? With sensitivity E1 Briefly touch various objects made of metal, plastic or wood around you with your fingertips. What do you feel Metals quickly dissipate heat when you touch them, drawing heat away from your fingers. Metals feel noticeably colder than wood or plastics at room temperature (Fig. 13.3). The reason for this is the different thermal conductivity of these materials ( page 100). Warmth helps! (Fig.13.4) E1 Fill a hot water bottle with very hot water (approx. 80 ° C) and feel the pleasant transport of heat to the palm of your hand. The water in the hot water bottle is a poor conductor of heat and a good heat store. The hot water bottle is made of rubber - another poor conductor of heat. The rubber only slowly transfers the heat to the body. Water-filled balloon over the candle (Fig.13.5) E1, E2 Hold a balloon filled with water and knotted over the candle flame for 1 minute. Will the balloon skin burst? The water absorbs the heat and protects the balloon skin. V3 plastic and air air air plastic spacer vacuum mirrored glass 13.1 Heat in good hands - the thermos flask 13.2 Windows with double glazing In a vacuum there is no conduction of heat. M V4 13.3 The door handle is a good conductor of heat and feels cooler than the poor conductor of heat, wood. Info box: Good heat conductors warm up quickly and cool down again quickly. Bad heat conductors stay warm for a long time after they have been heated - they store the heat. V5 13.4 Heat helps! V6 13.5 Water-filled balloon over the candle Whether a fabric feels warm or cold depends on its thermal conductivity. Good heat conductors feel cold, bad heat conductors feel warm. M 13.6 The air between the wool threads is a poor conductor of heat. Worksheets 9sd9e9 For testing purposes only - property of the publisher öbv