Reversible changes in Daily Life
Reversible changes in Daily Life
Relevance of Reversible Changes in Daily Life:
1. Working of Blacksmith: A blacksmith changes a piece of iron into different tools. For that, a piece of iron is heated to red hot. This also softens it. It is then beaten into the desired shape. It is a reversible change.
2. Expansion and contraction of metals: Metals expand on heating and contract on cooling. This expansion and contraction of a metal is a reversible change.Small gaps are left between the rails that form the parallel lines of a railway track. These gaps are called expansion gaps. These gaps allow the rails expand in hot weather. If there are no gaps or gaps are too small the lines can bend.
3. Fixing wooden handles on tools: While making agricultural tools the metal ring is heated before fixing the wooden handle. On heating the metal ring expands. When the ring become bigger size the wooden handle fix easily. When the metal ring cools, it contract and the handle fits in tightly.
4. Fixing metallic rim on a wooden wheel: The fixing of metallic rim to the wooden base of the wheel of bullock cart can be done in the similar manner. The metallic rim used is slightly smaller in diameter than the wheels .On heating the rim expands. And can easily lie on the wheels. When the rim cools, it contract and press tightly on to the wheels.
Note:
Burning of a candle is a chemical change whereas melting of wax is a physical change. When wax melts, it flows down and solidifies again. So, it is a reversible and temporary change. Thus, melting of wax is a physical change. On burning a candle, wax burns to produce wax vapour and carbon dioxide. It produces heat and light and candle becomes smaller on burning. New substances are formed energy is released during the burning of candle. It cannot reversed and it is a permanent change. Thus, burning of candle is a chemical change.
Metals expand on heating and contract on cooling, it is a _______________ change. | |||
| Right Option : A | |||
| View Explanation | |||
Which of the following are correct : (a) A piece of iron is heated to red hot which softens it and it is then beaten into the desired shape. It is a reversible change. (b) Burning of a candle is a chemical change whereas melting of wax is a physical change. (c) A piece of iron is heated to red hot which softens it and it is then beaten into the desired shape. It is a irreversible change. | |||
| Right Option : A | |||
| View Explanation | |||
__________________________ shows reversible change. | |||
| Right Option : D | |||
| View Explanation | |||
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