Scientific Reasons From Past Papers 19

➽ Why is the boiling point of sea water more than that of pure water?
Answer: Sea water contains salts and other impurities with different points which jointly rise its boiling point.

➽ Why is it recommended to add salt in water while boiling grams?
Answer: By addition of salt the boiling point of water gets which helps in cooking.

➽ Why is soft iron used as an electromagnet?
Answer: Because it remains magnetic only till the current passes through the coil and loses its magnetism when the current is switched off (principle of electric bells)

➽ Why does ink leak out of a partially filled pen when taken to a high altitude?
Answer: As we go up the pressure and the density of air go on decreasing. Partially filled pen leaks when taken to a higher altitude because the pressure of air acting on the ink inside the tube of the pen is greater than the pressure of air outside.

➽ Why does some liquids burn while others do not?
Answer: A liquid burns if its molecules can combine with oxygen of the air with the production of heat. Hence, oil burns but water does not.

➽ Oil and water do not mix. Why?
Answer: i) Molecules of oil are not bigger than that of water and therefore do not mix easily.
ii) Molecules of water are polar, i.e. they have opposite charges at two ends whereas oil molecules do
not; as a consequence they tend to stay away from water molecule.

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