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ICSE-VIII-Physics

06: Heat Energy Class 8 Physics

with Solutions - page 2

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  • #2-a
    Boiling occurs at _____
    Ans : Boiling occurs at a fixed temperature.
  • #2-b
    Evaporation takes place at ____
    Ans : Evaporation takes place at all temperature.
  • #2-c
    The molecules of liquid ____ heat from surroundings in evaporation.
    Ans : The molecules of liquid absorb heat from surroundings in evaporation.
  • #2-d
    Heat is _____ during boiling.
    Ans : Heat is absorbed during boiling.
  • #2-e
    Cooling is produced in _____.
    Ans : Cooling is produced in evaporation.
  • #2-f
    A longer rod expands _____ than a shorter rod on being heated to the same temperature.
    Ans : A longer rod expands more than a shorter rod on being heated to the same temperature.
  • #2-g
    Liquids expand _____ than the solids.
    Ans : Liquids expand more than the solids.
  • #2-h
    Gases expand _____ than the liquids.
    Ans : Gases expand more than the liquids.
  • #2-i
    Alcohol expands _____ than water.
    Ans : Alcohol expands more than water.
  • #2-j
    Iron expands _____ than copper.
    Ans : Iron expands less than copper.
  • Qstn #3
    Match the following
    Column A Column B
    (a) Blowing air Increases (i) Increase in inter-molecular separation
    (b) Increase in pressure increases (ii) pendulum of a clock
    (c) Thermal expansion (iii) cooking utensils
    (d) Invar (iv) boiling point
    (e) Pyrex glass (v) evaporation
    Ans :
    Column A Column B
    (a) A stone at a height (v) evaporation
    (b) A moving hall (iv) boiling point
    (c) Energy (i) Increase in inter-molecular separation
    (d) Power (ii) pendulum of a clock
    (e) watt (iii) cooking utensils
  • Qstn #4
    Select the correct alternative
  • #4-a
    In evaporation
    1. all molecules of liquid begin to escape out
    2. only the molecules at the surface escape out
    3. the temperature of liquid rises by absorbing heat from surroundings.
    4. the molecules get attracted within the liquid.
    digAnsr:   2
    Ans :
    2. only the molecules at the surface escape out
  • #4-b
    The rate of evaporation of a liquid increases when :
    1. temperature of liquid falls
    2. liquid is poured in a vessel of less surface area
    3. air is blown above the surface of liquid
    4. humidity increases.
    digAnsr:   3
    Ans :
    3. air is blown above the surface of liquid
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