Question : Why do two eyes give better vision than one?
Answer : Because two eyes do not form exactly similar images and the fusion of these two dissimilar images in the brain gives three dimensions of the stereoscopic vision.

Question : Why does water remain cold in an earthen pot?
Answer : There are pores in an earthen pot which allow water to percolate to the outer surface. Here evaporation of water takes place thereby producing a cooling effect.

Question : Why do we place a wet cloth on the forehead of a patient suffering from high temperature?
Answer : Because of body’s temperature, water evaporating from the wet cloth produces a cooling effect and brings the temperature down.

Question : When a needle is placed on a small piece of blotting paper which is placed on the surface of clean water, the blotting paper sinks after a few minutes but the needle floats. However, in a soap solution the needle sinks. Why?
Answer : The surface tension of clean water being higher than that of a soap solution, it can support the weight of a needle due to its surface tension. By addition of soap, the surface tension of water reduces, thereby resulting in the sinking of the needle.

Question : To prevent multiplication of mosquitoes, it is recommended to sprinkle oil in the ponds with stagnant water. Why?
Answer : Mosquitoes breed in stagnant water. The larvae of mosquitoes keep floating on the surface of water due to surface tension. However, when oil is sprinkled, the surface tension is lowered resulting in drowning and death of the larvae.

Question : Why does oil rise on a cloth tape of an oil lamp?
Answer : The pores in the cloth tape suck oil due to the capillary action of oil.

Question : Why are ventilators in a room always made near the roof?
Answer : The hot air being lighter in weight tends to rise above and escape from the ventilators at the top. This allows the cool air to come in the room to take its place.

Question : How does ink get filled in a fountain pen?
Answer : When the rubber tube of a fountain pen immersed in ink is pressed, the air inside the tube comes out and when the pressure is released the ink rushes in to fill the air space in the tube.

Question : Why are air coolers less effective during the rainy season?
Answer : During the rainy reason the atmospheric air is saturated with moisture. Therefore, the process of evaporation of water from the moist pads of the cooler slows down thereby not cooling the air blown out from the cooler.

Question : Why does grass gather more dew in nights than metallic objects such as stones?
Answer : Grass being a good radiator enables water vapour in the air to condense on it. Moreover, grass gives out water constantly (transpiration) which appears in the form of dew because the air near grass is saturated with water vapour and slows evaporation. Dew is formed on objects which are good radiators and bad conductors.

Question : If a lighted paper is introduced in a jar of carbon dioxide, its flame extinguishes. Why?
Answer : Because carbon dioxide does not help in burning. For burning, oxygen is required.