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ICSE-IX-Physics

06: Heat and Energy

with Solutions -

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    Section : A
  • Qstn #1
    What is heat? Write its S.I. unit.
    Ans : Heat is the energy of random motion of molecules constituting the body.
    Its S.I. unit is ‘joule’.
  • Qstn #2
    Two bodies at different temperatures are placed in contact. State the direction in which the heat will flow.
    Ans : Heat will flow from a hot body (body at a higher temperature) to a cold body (body at a lower temperature)
  • Qstn #3
    Name the S.I. unit of heat and how is it related to the unit calorie?
    Ans : S.I. unit of heat is ‘joule’.
    1 joule = 0.24 cal
  • Qstn #4
    Define temperature and write its S.I. unit.
    Ans : Temperature is the parameter which tells the thermal state of a body (i.e. the degree of hotness or coldness).
    The S.I. unit of temperature is ‘kelvin’
  • Qstn #5
    Why does a piece of ice feel cool to touch? Explain.
    Ans : On touching a piece of ice, heat flows from our hand (hot body) to the ice (cold body), and hence, it appears cold.
  • Qstn #6
    Distinguish between heat and temperature.
    Ans : Heat is a form of energy obtained due to the random motion of molecules in a substance but temperature is a quantity which decided the direction of flow of heat when two bodies at different temperature are placed in contact. Two quantities having the same amount of heat may differ in temperature..
  • Qstn #7
    What do you understand by thermal expansion of a substance?
    Ans : The expansion of a substance on heating is called thermal expansion.
  • Qstn #8
    Name two substances which expands on heating.
    Ans : Brass and iron expand on heating.
  • Qstn #9
    Name two substances which contract on heating.
    Ans : Water contracts on heating from 0 to 4.
    Silver iodide contracts on heating from 80 to 141.
  • Qstn #10
    What do you mean by the anomalous expansion of water?
    Ans : The expansion of water when it is cooled from 4 to 0 is known as the anomalous expansion of water.
  • Qstn #11
    At what temperature is the density of water maximum? State its value.
    Ans : Density of water is maximum at 4. Its value is 1000 kgm-3.
  • Qstn #12
    State the volume changes that you will observe when a given mass of water is heated from 0°C to 10°C . Sketch a temperature-volume graph to show the behaviour.
    Ans : When a given mass of water is heated from 0°C to 4°C, it contracts, i.e. its volume decreases.
    On heating from 4°C to 10°C , it expands, i.e. its volume increases.
  • Qstn #13
    Draw a graph to show the variation in density of water with temperature in the range from 0°C to 10°C.
    Ans :
  • Qstn #14
    A given mass of water is cooled from 10°C to 0°C . State the volume changes you will observe. Represent these changes on a temperature-volume graph.
    Ans :
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