HomeLearn Fast select Course
Change UnitChange SubjectLast Menu
ICSE-VIII-Physics

06: Heat Energy Class 8 Physics

with Solutions - page 5

Note: Please signup/signin free to get personalized experience.

Note: Please signup/signin free to get personalized experience.

10 minutes can boost your percentage by 10%

Note: Please signup/signin free to get personalized experience.

  
  • Qstn #18
    State three factors on which depend the linear expansion of a metal rod on heating.
    Ans : Factors on which increase in length of a rod depend when heated are:
    1. Length of rod L. Increase in length is directly proportional to original length.
    2. Temperature of rod. It is directly proportional to increase in temperature.
    3. Nature of material of rod.
    If L1 is original length of rod at t1 °C and on heating to t2 °C its length becomes L2.
    ∴ Increase in length of rod = (L2 - L1)
    and increase in temperature (t2 - t1)
    ∴ [L2 - L1] ∝ L1 (t2 - t1)
    But the increase in length of rod does not depend on whether the rod is solid or hollow.
  • Qstn #19
    Two iron rods - one 10 m long and the other 5 m long, are heated to the same rise in temperature. Which will expand more ?
    Ans : Lt - L0 ∝ L0
    ∴ The rod having greater length will expand more when rods are heated to the same
    temperature.
    ∴ Rod with 10 m length will expand more.
  • Qstn #20
    Two identical rods of copper are heated to different temperatures one by 5°C and the other by 10°C. Which rod will expand more ?
    Ans : Two rods with same length and material are heated to different temperature.
    Lt-L0 ∝ t
    ∴ Rod with higher temperature i. e. at 10°C will expand more.
  • Qstn #21
    One rod of copper and another identical rod of iron are heated to the same rise in temperature. Which rod will expand more? Give reason.
    Ans : When two identical rods (same length) are of different material and heated to same rise in temperature, the copper rod will expand more than iron, since expansion depends on nature of material.
    (Coefficient of linear expansion of copper 17 ×10-6 per °C > iron 13 ×10-6 per °C)
  • Qstn #22
    Two identical rods- one hollow and the other solid, are heated to the same rise in temperature. Which will expand more ?
    Ans : When two identical rods are heated to the same range of temperature, solid rod will expand more.
    More heat is present in solid rod.
  • Qstn #23
    In the ball and ring experiment, if the ball after heating is left to cool on the ring for some time, the ball again passes through the ring. Explain the reason.
    Ans : On heating the ball expands and increases in size and cannot pass the ring when left on it. As the ball cools, it contracts, size becomes less than ring and passes the ring.
  • #24-a
    The telephone wires break in winter.
    Ans : Metals expand on heating (in summer) and contract on cooling (in winter). Therefore while putting up the wires between two poles, care is taken that they are kept tight while laying them in winter as they sag in summer due to expansion.
  • #24-b
    Iron rims are heated before they are fixed on the wooden wheels.
    Ans : Iron rims are made slightly smaller in diameter than the wooden wheel and on heating wheel expands and can easily slip over the wooden wheel and on cooling the rim contracts and makes a tight fit over the wooden wheel.
  • #24-c
    The gaps are left between the successive rails on a railway track.
    Ans : In summer due to considerable rise in temperature, the gaps allow for the expansion of rails, otherwise the rail will bend side ways.
  • #24-d
    A glass stopper stuck in the neck of a bottle can be removed by pouring hot water on the neck of the bottle.
    Ans : By pouring hot water on the neck of the bottle, the neck expands and stuck glass stopper can easily be removed.
  • #24-e
    A cement floor is laid in small pieces with gaps in between.
    Ans : In summer when temperature rises small pieces of cement expand and to allow expansion gaps are left between small pieces.
  • Qstn #25
    Why is one end of a steel girder in a bridge kept on rollers instead of fixing it in pillar ?
    Ans : In summer when temperature increases considerably the bridge made of metal expands
    and rollers slide to allow for expansion otherwise the bridge may break the pillar.
  • Qstn #26
    A metal plate is heated. State three factors on which the increase in its area will depend.
    Ans : Three factors are:
    1. Original area of plate A0.
    2. Rise in temperature t.
    3. Nature of material of plate.
  • Qstn #27
    A cubical metal solid block is heated. How will its volume change ?
    Ans : When a solid is heated, it expands in all directions. The volume of a cube also increases.
    Let V0 be the volume of cube of side L0 at 0°C. i.e. V0 = L30 - V
    When temperature increases to t°C each side increases to Vt
    ∴ Vt = Lt3
    Increase in volume = (Vt — V0) [Lt3 - L30]
    Increase in temperature = (t - 0)°C = t°C
next page