Question

Q3. Give reasons for the following:
a. Electrical wires are covered with rubber or plastic
b. Gold and silver are used to make jewellery.
A wooden plank floats on water.
d. When we add sugar to water and stir it, it disappears.
e. Metallic objects lose their lustre after some time​

Answer 1

Answer:

1. Most electrical wire is covered in a rubber or plastic coating called insulation. ... The purpose of insulation covering the metal part of an electrical wire is to prevent accidental contact with other conductors of electricity, which might result in an unintentional electric current through those other conductors.
2. Gold and silver are used to make jewellery because they are precious and expensive metals. It is easier to obtain metals from their oxides rather than from carbonates or sulphides. So the ore is first converted into an oxide.
3. Wood floats on water as per principle of buoyancy defined by Archimedes — that the water displaced equals the weight of the wood.
4. Sugar gets disappeared once added to water. This is because sugar is a substance that is soluble in water. We know that soluble substances disappear in water after getting dissolved completely. Hence the sugar disappears.
5. Metals react with the atmosphere oxygen and the oxygen is bonded to them. after a layer of oxide forms over the surface, the metals lose their lustre. this does not happen in case of metals like Platinum and gold as it is difficult to oxidise them.

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