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Chapter – 4 Heat Heat: It is a form of energy, which makes any object hot or cold. Temperature: The degree of hotness of an object is called temperature. Oursense of touchis not reliable to measure thetemperature. Thermometer is a device used for measuring temperatures. Heatis the cause of temperature. Clinical thermometer isused to measure our body temperature. The range ofthis thermometer is from 35°C to 42°C. For other purposes, we use the laboratory thermometers. The range of these thermometers is usually from –10°C to 110°C. The normal temperature of thehuman body is37°C. The materials which allow heat to pass through them easily are conductors of heat. The materials which do not allowheat to passthrough them easily are called insulators. Clinical Thermometer: It is a thermometer used to measure the temperature of our body. It consists of a long, narrow, uniform glass tube with a bulb containing mercury at one end. There is a kink near the bulb. It reads a range of temperatures from 94°F to 108°F(35°C and42°C). Laboratory Thermometer: It is a thermometer used to measure the temperature of objects other than our body. It consists of a column of mercury enclosed in a glass casing. The column is continuous without any kink. It measures a range of temperature from-10˚C to 110˚C Sea Breeze: Durign the day, the land heats up faster than the sea. Warm air above the land rises and cold air from sea takes its place. Warm air from the land moves towards the sea to compele the cycle. Thisproduces a seabreeze from thesea to theland. Land Breeze: At night the land cools faster than sea. The warm airabove the searises. This warm airis replaced bycolder air fromthe land producing a land breeze
Transfer of Heat: Heat flows from a hotter object to a colder object until both objects reach thesame temperature. The heat flows from a body at a higher temperature to a body at a lower temperature. There are three ways in which heat can flow from one object to another. These are conduction, convection and radiation. Conduction: It is the process by which heat is transferred from the hotter end to the colder andend of anobject. Convection: It is the flowof heat through a fluid fromplaces of higher temperature to places of lower temperature by movement ofthe fluid itself. Radiation: It is the mode of transfer of heat in which energy is directly transferred from oneplace to another. It does notneed any material medium. Dark-coloured objects absorb radiation better than the light-coloured objects. That is the reason we feel morecomfortable in light-coloured clothes in thesummer. Woollen clothes keep us warmduring winter. It is so because woolis a poor conductor of heatand it hasair trapped inbetween the fibres.
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