CLASS 8 PHYSICS CHAPTER 6 HEAT TRANSFER EXERCISE SOLUTIONS Test Your Understanding [Page No. 101] Question : Tick the correct option : 1. When heat is constantly supplied by a burner to boiling water, then the temperature of water during vaporisation Answer : (d) does not rise at all 2. The evaporation of water increases under the following conditions Answer : (c) increase in surface area, rise in temperature 3. If surface area of liquid is large then evaporation will be Answer : (b) more 4. Changing of a liquid into vapours from the surface without heating it is called Answer : (c) evaporation 5. Evaporation takes place at Answer : (d) at all temperatures Test Your Understanding [Page No. 105] 1. The length of an iron rod increases from 10 m to 11 m, when kept over a burner flame. This increase in length is due to Answer : (b) linear expansion 2. Gaps are left in railway tracks to compensate thermal expansion during Answer : (c) hot season 3. An increase in breadth, length and thickness of a substance is due to Answer : (b) thermal expansion 4. An automatic fire alarm is a Answer : (b) heat detector 5. Wires on electric poles are given some sag to prevent breaking in Answer : (a) winter EXERCISES A. Choose the correct option : 1. Evaporation takes place from : Answer : (a) surface of the liquid 2. Changing of a liquid into vapours at a fixed temperature is called Answer : (b) boiling 3. Which of the following is correct in case of thermal expansion? Answer : (b) A longer rod of a metal expands more than a smaller rod of the same metal 4. Boiling point of water is Answer : (b) 1000C 5. Evaporation from surface of any liquid depends on Answer : (d) all of above 6. Volume thermal expansion is also termed as : Answer : (d) cubical thermal expansion 7. At high temperature, evaporation is Answer : (a) fast B. Fill in the blanks : 1. Change of state of a liquid into gas at constant temperature is called . Answer : boiling 2. Evaporation is followed by .effect. Answer : cooling 3. Boiling is a .phenomena. Answer : bulk 4. Increase in length of an iron rod on heating is termed as Answer : linear expansion 5. The coefficient of thermal expansion depends on of the substance. Answer : nature
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