Qstnid -B-24-a-the Telephone Wires Break In Winter. (B) Iron Rims Are Heated Before They Are Fixed On The Wooden Wheels. (C) The Gaps Are Left Between The Successive Rails On A Railway Track. (D) A Glass Stopper Stuck In The Neck Of A Bottle Can Be Removed By Pouring Hot Water On The Neck Of The Bottle. (E) A Cement Floor Is Laid In Small Pieces With Gaps In Between. - 06: Heat Energy Class 8 Physics

with Solutions - page 5

#24-a
The telephone wires break in winter. (b) Iron rims are heated before they are fixed on the wooden wheels. (c) The gaps are left between the successive rails on a railway track. (d) A glass stopper stuck in the neck of a bottle can be removed by pouring hot water on the neck of the bottle. (e) A cement floor is laid in small pieces with gaps in between.
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. (b) 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. (c) In summer due to considerable rise in temperature, the gaps allow for the expansion of rails, otherwise the rail will bend side ways. (d) By pouring hot water on the neck of the bottle, the neck expands and stuck glass stopper can easily be removed. (e) In summer when temperature rises small pieces of cement expand and to allow expansion gaps are left between small pieces.

#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.