Name and explain any five physical changes.
1. Change of physical state: Solids can be converted into liquid and then to a gas by heating or vice-versa.
2. Glowing of an electric bulb: When a bulb is switched on, its filament made of tungsten starts glowing. When the bulb is switched off, the bulb stops glowing and there is no change in its filament.
3. Dissolution of salts: When common salt is added to water, a solution is formed. When the solution is heated, water evaporates and white solid of common salt is left behind. This white solid has the same properties as the original substance.
4. Mixing of iron filings and sulphur: If the iron filings are separated from sulphur with the help of a magnet, the properties of the substances recovered are the same as the original substances, i.e., iron filings and sulphur.
5. Sublimation of naphthalene: When naphthalene is heated, it gets converted into vapours which are sublimed (condensed) into a white solid, which has the same properties as the original substance.
