SCIENTIFIC REASONING QUESTIONS FOR ALL COMPETITIVE EXAMS
91) Why is spring made of steel and not copper?
Ans: The elasticity of steel is greater than that of copper.
Ans: The elasticity of steel is greater than that of copper.
92) Why is it easier to spray water to which soap is added?
Ans: Addition of soap decreases the surface tension of water. The energy for spray is directly
proportional to surface tension.
93) A piece of chalk when immersed in water, emits bubbles. Why?
Ans: Chalk consists of pores forming capillaries. When it is immersed in water, the water begins to
rise in the capillaries and air present there is expelled in the form of bubbles.
94) Why does a liquid remain hot or cold for a long time inside a thermo flask?
Ans: Because of the presence of air, which is poor conductor of heat, in between the double glass
walls of a thermos flask.
95) Why is the boiling point of sea water more than that of pure water?
Ans: Sea water contains salts and other impurities with different points which jointly rise its boiling
point.
96) Why is it recommended to add salt in water while boiling grams?
Ans: By addition of salt the boiling point of water gets which helps in cooking.
97) Why is soft iron used as an electromagnet?
Ans: 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)
98) Why does ink leak out of a partially filled pen when taken to a high altitude?
Ans: 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.
99) Why does some liquids burn while others do not?
Ans: 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.
100) Oil and water do not mix. Why?
Ans: 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.
Ans: Addition of soap decreases the surface tension of water. The energy for spray is directly
proportional to surface tension.
93) A piece of chalk when immersed in water, emits bubbles. Why?
Ans: Chalk consists of pores forming capillaries. When it is immersed in water, the water begins to
rise in the capillaries and air present there is expelled in the form of bubbles.
94) Why does a liquid remain hot or cold for a long time inside a thermo flask?
Ans: Because of the presence of air, which is poor conductor of heat, in between the double glass
walls of a thermos flask.
95) Why is the boiling point of sea water more than that of pure water?
Ans: Sea water contains salts and other impurities with different points which jointly rise its boiling
point.
96) Why is it recommended to add salt in water while boiling grams?
Ans: By addition of salt the boiling point of water gets which helps in cooking.
97) Why is soft iron used as an electromagnet?
Ans: 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)
98) Why does ink leak out of a partially filled pen when taken to a high altitude?
Ans: 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.
99) Why does some liquids burn while others do not?
Ans: 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.
100) Oil and water do not mix. Why?
Ans: 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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