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ICSE-VIII-Physics

06: Heat Energy Class 8 Physics

with Solutions - page 7

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  • Qstn #28
    Describe an experiment to show that liquids expand on heating.
    Ans : Experiment:
    • Take round bottomed flask filled with water.
    • Close its mouth with air-tight cork having delivery tube through it.
    • Mark the level of water. Let it be at A.
    • Now heat the flask. As water gets heated in flask, the level of water in the tube rises from A to B.
    • This proves that liquids expand on heating.


    ORExperiment:
    • Take a laboratory Celsius thermometer Suspend it with the help of a stand.
    • Note the level of mercury thread in it. Let it be at A.
    • Now take hot water in a beaker and as shown, set up the arrangement.
    • The mercury thread rises to B by gaining temperature.
    • This shows that liquids expand on heating.

  • Qstn #29
    State one application of thermal expansion of liquids.
    Ans : Application of Thermal Expansion of Liquids:
    • An important application is mercury thermometer or alcohol thermometer.
    • When the bulb of the thermometer is kept in contact with a hot body the mercury expand and the level of mercury rises in the capillary tube.
  • Qstn #30
    Describe an experiment to show that air expands on heating.
    Ans :
    • Take a glass flat bottomed flask.
    • Close its mouth with a cork having capillary tube containing indicator visible in the tube as shown.
    • Make it air tight. Place the flask in hot water.
    • After few minutes, we see the indicator moving up.
    • This happens because air inside the flask expands with rise in temperature.
    • This proves that gases expand on heating.

  • Qstn #31
    An empty glass bottle is fitted with a narrow tube at its mouth. The open end of the tube is kept in a beaker containing water. When the bottle is heated, bubbles of air are seen escaping into water. Explain the reason.
    Ans : When the bottle is heated, air in it expands and escapes the water in the form of bubbles.
  • Qstn #32
    Which of the following will expand more, when heated to the same temperature :
    - (a) solid
    (b) liquid and
    (c) gas?
    digAnsr:   c
    Ans : (c) Gas will expand more as the inter-molecular force of attraction in gas molecules is least and K.E. is maximum.
  • Qstn #33
    Describe an experiment to show that same volume of different liquids heated to same rise in temperature expand by different amounts.
    Ans : Cubical Expansion of different Liquids is different:

    Experiment: Take four identical glass flasks each fitted with a narrow glass tube through a cork at its mouth. Fill flask A with water, B with kerosene, C with alcohol and D with Benzene. So that volume of each is same i.e. to the same level and their levels are visible above hot water bath. Put enough hot water in hot-water-bath. So that each flask is in the hot water. After some time we will see that different liquids rise to different levels. Water expands the least and benzene the most. This shows that different liquids of same volume expand by different amount.
  • Qstn #34
    100 ml of each of the following liquid is heated from 10°C to 50°C. Which will expand more :
    - (a) water
    (b) benzene
    (c) alcohol ?
    digAnsr:   b
    Ans : (b)
    100 ml. of each means same volume of each liquid heated 10°C to 50°C means same rise in temperature. Hence, Benzene will expand more Water will expand least.
  • Qstn #35
    Water is heated from 0°C to 4°C. Will it expand ?
    Ans : Substances expand on heating.
    But water contracts with heated from 0°C to 4°C. After that i.e. above 4°C water starts expanding.
  • Qstn #36
    What do you mean by anomalous behaviour of water ?
    Ans : Substances when heated expand. Their density [m/v] decrease. But in case of water:
    When water is heated from 0°C to 4°C it contract and density increases, heating water above 4°C starts expanding and density of water decrease. This means water has maximum density at 4°C. This is called anomalous behaviour of water.
  • Qstn #37
    How does the density of a substance (solid, liquid and gas) change on heating ?
    Ans : Density = Mass/Volume
    In case of solids, when temperature is increased, increase in volume is very small and decrease in density is not appreciable. In case of liquids and gases, as the temperature increases, volume increases by an appreciable amount and therefore decrease in their density is quite considerable.
  • Qstn #38
    An iron washer is heated. State the effect on its
  • #38-i
    mass,
    Ans : Mass remains same on heating.
  • #38-ii
    internal diameter,
    Ans : Internal diameter increases.
  • #38-iii
    external diameter, and
    Ans : External diameter increases.
  • #38-iv
    density.
    Ans : Density decreases.
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