Ncert- science – class 7- Chapter 3 – Heat 2 Welcome to your Ncert- science - class 7- Chapter 3 – Heat 2 1. Lake water never completely freezes because none of the above Principle of conduction prevents it both of the above Principle of convection prevents it None 2. In experiment of heat transfer by convection, water inside the pipe completely gets heated (with the application of heat source). This can be explained best by which of the following statements, A continuous conductive channel is produced between the different layers of water in the pipe which circulates the heat. all of the above both the above explains correctly Differences in densities produced between the bottom and the top of water , in turn produce the driving force which continuously circulates the water. None 3. Choose the correct answer from the alternatives given :For measuring very high temperature, we use Mercury thermometer Platinum resistance thermometer Thermoelectric pyrometer None of the above None 4. Two thermometers are constructed in the same way except that one has a spherical bulb and the other a cylindrical bulb; which one will respond quickly to temperature changes? Cylindrical bulb thermometer both equally either Spherical bulb thermometer None 5. Beaker A contains hot water. Beaker B contains cold water. Beaker C contains a mixture of hot and cold water. If initially your hand is put into a beaker containing ice, then putting your hand in which of the beakers A, B or C will give a sensation of warmth? All of the above. A B C None 6. Suppose a liquid in a container is heated at the top rather than at the bottom. What is the main process by which the rest of the liquid becomes hot ? None of these Evaporation Sublimation Conduction None 7. What is the use of kink near the bulb in clinical thermometer? It prevents the level of the mercury from falling when taken out of the mouth It prevents the level of the mercury from rising when taken out of the mouth It allows the level of the mercury to rise when taken out of the mouth It allows the level of the mercury to fall when taken out of the mouth None 8. A laboratory thermometer is dipped in a beaker containing ice. As the thermometer is removed the mercury level will either rise or fall depending upon how much ice is kept inside the beaker neither rise nor fall fall rise None 9. A long silver tea spoon is placed in a cup filled with hot tea. After some time, the exposed end (the end which is not dipped in tea) of the spoon becomes hot even without a direct contact with the tea. This phenomenon can be explained mainly by_______ reflection conduction radiation thermal expansion None 10. A laboratory thermometer is dipped in a beaker containing hot water. As the thermometer is removed the mercury level will it may rise or fall depending upon how much water is kept inside the beaker neither rise nor fall rise fall None 11. Two thin blankets are warmer than one blanket of their combined thickness, this happens, because Double layer prevent transmission of heat Two blankets have large mass one blanket is heavier None of the above None 12. The rise in temperature of a substance depends on the mass of the substance the nature of the substance the quantity of heat supplied all the above None 13. Identify the statement in which the mode of heat transfer is convection ? Ice cubes cooling a drink A microwave oven cooking a meal The heat of the sun warming our planet The heat from an electric stove warming a frying pan None 14. A red hot brick is placed on an iron tripod stand which stands on a large block of copper. The brick loses heat by: conduction and convection conduction conduction, convection, and radiation conduction and radiation None 15. On a cold day when a room temperature is 15 degree C, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15 degree C, because metals are good conductor of heat plastics have a higher thermal conductivity than metals plastics have a lower density than metals metals have higher thermal capacity than plastics None 16. In which of the following processes, convection does not take place primarily? Heating air around a furnace Boiling of water Warming of glass of bulb due to filament Sea and land breeze None 17. Which of the following is not true about Laboratory thermometers ? Laboratory thermometers are used to measure body temperature. Range of laboratory thermometer is -10C to 110C Laboratory thermometers are used to measure temperatures with a high degree of precision. Laboratory thermometers are designed for lab purposes such as checking boiling point, freezing point etc. None 18. Which of the following minimizes the transference of heat in a thermos flask?1. Conduction2. Convection3. Radiation 2 and 3 1 and 3 1,2,and 3 1 and 2 None 19. An ideal thermometer should have Large heat capacity Medium heat capacity Small heat capacity Variable heat capacity None 20. Among the following what should not be done while or before using a clinical thermometer? Ensure that before use the mercury level is below 35 degree C Handle the thermometer with care, as you handle any glass articles. Don't hold the thermometer by the bulb while reading it. Wash the thermometer with hot water. 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