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9. HEAT, Q1: Fill in the blanks with the proper word from the brackets., (radiation, white, conduction, blue, convection, bad conductor, good conductor, black,, reflection), (a) Maximum heat is absorbed by a black coloured object., (b) Radiation of heat does not require a medium., (c) Conduction of heat takes place through a good conductor substance., (d) The shining surface in a thermos flask decreases the outgoing heat by reflection., (e) Cooking utensils are made from metals due to their property of conduction., (f) The earth receives heat from the sun by radiation., , Q2: What will absorb heat?, Steel spoon, wooden board, glass vessel, iron griddle (tava) , glass, wooden spoon ,, plastic plate, soil, water, wax, Ans) Steel spoon, iron griddle, water, soil and wax will absorb heat., , Q3: Write answers to the following question :, (a) How does a fever get lowered by putting a cold compress on the forehead of a, patient ?, Ans) Cold compress is made up of material that absorbs heat. Hence it absorbs heat, from the patient's body and lowers the body temperature., (b) Why are the houses in Rajasthan painted white ?, Ans) Rajasthan is a very hot place and white colour is a reflector of heat. Hence houses, are with their walls painted white so that most of the heat from the Sun is reflected back, to the atmosphere. This keeps the houses cool from inside., (c) What are the modes of heat transfer ?, Ans) There are three modes of heat transfer:, ● Conduction, ● Convection, ● Radiation

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(d) Which mode of heat transfer causes sea breezes and land breezes., Ans) Convection causes sea breeze and land breeze., (e) Why is the outer coat of the penguins of Antarctica black ?, Ans) Black colour is a good absorber of heat. So, in cold regions like Antarctica, the, black outer coating of Penguins helps them to absorb as much heat from the, surroundings and keep their bodies warm., (f) Why are heaters fitted near the floor and air conditioners, near the ceiling of a room ?, (f) Room heaters are fitted near the floor because this allows the hot air near the heater, to rise up and warm the entire room., The air conditioners are fitted near the ceiling, so that the cold air from the AC takes the, place of hot air rising up from the bottom. In this way, the entire room gets cooled., Q.4) Give scientific reasons., (a) The telephone wires which sag in summer become straight in winter., An) In summers, the surrounding temperature is very high. Due to this high temperature,, the metallic telephone wires are heated up and thus expands in length. Due to this, they, sag down., In winters, the surrounding temperature is very low. Due to this low temperature, the, metallic telephone wires are cooled down and thus contracts in length. Due to this, they, become straight., (b) Dew drops form on the grass in winter., Ans) In winters, the temperature of the air near the grass decreases to dew point. Thus,, the air becomes saturated with water vapour. As a result, water vapour condenses into, tiny water droplets which appear on the surface of the grass.