5. Give reasons for the following

1. An ordinary glass bottle cracks when boiling water is poured into it, but a borosilicate glass bottle does not. 

  

Borosilicate glass is a type of glass which has a unique quality of providing a very low coefficient of thermal expansionvery high coefficient of thermal expansion. This refers that it will not crackwill crack under extreme high-temperature changes like the regular glass does. The durability of borosilicateregular glass glass has made it very popular in the research laboratories.

 

2. The electric wire which sag in summer become straight in winter.

 

The telephone wires sag in summer due to contractionexpansion and become tight due to the expansioncontraction. This happens because the cores of the wires are made from plasticcopper.

 

3. Rivet is heated before fixing in hole to join two metal plates.

 

A rivet is made up of ductile steelbrittle steel with a head at the one end. It is made up of steel with low tensilehigh tensile steel. The rivet is used for connecting pieces of metal and is made of steel with low tensilehigh tensile strength. For using the rivets, they are heated till they become hot red and are then they are placed in the hole.