Ans. No, the change cannot be reversed as it is an irreversible change.
Ans. A piece of iron is heated till it becomes red and hot and then it becomes soft and is beaten into desired shape and size.
Ans. Setting of curd is an irreversible change because new substance (curd) formed cannot be converted back into milk again.
Ans. Burning of incense stick is an irreversible change because when incense stick are burnt, new substances are produced in the form of ash and smoke which cannot be converted back into incense stick again.
Ans. A candle reduces in size on burning because wax near the wick melts into a liquid and changes into ash and fumes. It is an irreversible change as new substance formed cannot be converted back to candle again.
Ans. Metals expand on heating and contract on cooling. Iron rims are made slightly smaller than the wheels. Rim is heated so that it expands and lies easily on the wheels. The same rim, on cooling contracts and get firmly fixed on the wheels.
Ans.
Slow Change |
Fast Change |
1. The changes that take place in long period of time are called Slow change. |
1. The changes that take place in short period of time are called Fast change. |
2. Examples: germination of seed, curdling of milk, mountain formation, rusting of iron etc. |
2. Examples: burning of paper, burning of candle, thunderstorm, bursting of crackers etc. |
Ans. Formation of clouds is a physical change because water evaporates by the process of evaporation and goes into air and form clouds by the process of condensation. This water again comes back to the earth by precipitation. This process is repeated again and again.
Ans.
Frying a puri |
Rolling a puri |
1. It is an Irreversible change. |
1. It is reversible change. |
2. Taste and color will change. |
2. Shape and size will change. |
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