Scientific, Geographical and Astronomical Phenomena
(Questions and Answers)
Q. Why does a piece of iron get rusted if left exposed in the open ?
Ans. Iron piece rusts if left exposed in the open because it reacts with the oxygen in the air, forming iron oxide�a compound of Iron and oxygen.
Q. Why can petrol fire not be put out with water ?
Ans. Petrol is a hydro carbon which remains isolated with water and is having less density. So when water is poured petrol floats on it and keeps on burning. The temperature of the burning petrol is so high that the water poured on the petrol fire is evaporated before it extinguishes the fire.
Q. Ice packed is saw dust does not melt quickly. Why ?
Ans. Saw dust is a bad conductor of heat and protects the ice from the external heat and hence from melting away quickly.
Q. White light passing through a glass prism gives rise to a coloured pattern on the wall. Why ?
Ans. White light is made up of seven colours. Rays of different colours refract or bend along different paths and fall on different points on the wall forming a coloured pattern known as spectrum.
Q. A boatman pushes the bank with his pole. Why ?
Ans. Action and reaction being equal and opposite, the bank will push the boat away from it.
Q. A burning candle gets extinguished when covered with a tumbler. Why ?
Ans. A burning candle gets extinguished when covered with a tumbler because the supply of oxygen is cut-off and the flame goes out.
Q. Why do you see rainbow after rain ?
Ans. The water drops suspended in the atmosphere act as prism and disperse light into seven colours.
Q. A metal tea-pot has an ebony handle. Why ?
Ans. Ebony being bad conductor of heat, the handle does not get hot.
Q. Why is one�s breath visible in winter, but not in summer ?
Ans. In winter the water vapour contained in the breath condenses into small droplets of water, which become visible. In summer it is not so.
Q. The weight of a man on the surface of the moon will be only about one-sixth of his weight on the earth. Why ?
Ans. The gravity of the moon is one-sixth that of the earth, hence the weight of a person on the surface of the moon will be onesixth of his weight on the earth.
Q. Why is it easier to roll a barrel than to pull it along the road ?
Ans. Slipping resistance is much more than rolling resistance.
Q. Why is the flash of lightning seen before the sound of thunder is heard ?
Ans. Because light travels faster than sound.
Q. How does a soda water straw work ?
Ans. When we suck through a soda water straw, low pressure is created inside the straw. The liquid outside rushes into balance the difference.
Q. Small space is left between each set of two rails of a railway line.
Ans. Iron expands when it gets hot. A small space is left between the ends of the rails in order to allow the expansion of rails due to heat.
Q. How does bulb emit light ?
Ans. The current passes through a wire of high resistance which becomes red hot, and emits light.
Q. What is an electric fuse ? What purpose does it serve ?
Ans. A thin wire used in maintaining the condition of the energy; it prevents overloading of energy.
Q. How does a thermos flask keep a hot liquid hot and cold liquid cold ?
Ans. It is a double-walled vessel in which the inner surface of the outer vessel and the outer surface of the inner vessel are silvered so as to prevent radiation of heat. The space between the walls of the two vessels is made of vacuum to prevent the escape of heat by conduction or convection.
Q. A parachute enables a person to descend in safety in case of an accident to aircraft ?
Ans. A man falls to the earth because of the gravitational pull of the earth. The parachute offers considerable resistance to that gravity, thereby slowing down the speed of the descending man. The parachute thus enables a person to descend in safety.
Q. A person in a moving vehicle is thrown forward when the vehicle stops suddenly. Why ?
Ans. When a moving vehicle stops suddenly, a passenger will tend to fall forward because the lower part of his body in contact with the seat comes to stop suddenly but the upper part of his body is still in motion sharing the movement of the train. So on account of inertia, the passenger falls forward.
Q. A plane approaching at a speed of 1000 m.p.h. is not heard. Why ?
Ans. Sound travels at a speed of 760 m.p.h., hence a plane approaching at a speed of 1000 m.p.h. cannot be heard.
Q. Why does an electric bulb make a bang when it is broken ?
Ans. An electric bulb has a partial vacuum. When it is broken, air rushes into take the place of the vacuum, hence it bangs.
Q. Why does a ship made of steel float though a steel ball sinks ?
Ans. The ship displaces more water then its own weight whereas the weight of the water displaced by a steel ball is much less than the weight of the steel ball.
Q. Why do the stars twinkle ?
Ans. The stars seem to twinkle due to two causes. First the light from the stars passes through several mediums; secondly our vision has a tendency to distract.
Q. Why is it easier to swim in a sea than in a river ?
Ans. The density of the sea water is higher than the density of the river water.
Q. Why is hot soup more tasty than the colder one ?
Ans. As temperature is increased, surface tension decreases and the liquid now occupies more area. Thus the hot soup occupies more area on the tongue and is, therefore, more tasty than the colder one.
Q. Thick glass tumblers often crack when very hot liquids are poured into them. Why ?
Ans. The inner layer tends to expand more rapidly than the outer layer thus producing phenomenon of unequal expansion resulting in cracks due to the resulting pressure.
Q. Why does water get cooled in an earthen pitcher ?
Ans. Pitchers have pores through which water percolates which evaporates. During evaporation heat is taken away and the water gets cooled.
Q. Why does the sky and the water of the ocean look blue ?
Ans. The blue part of the sunlight is scattered by the particles of the atmosphere around, while other parts of light pass through it : that is why the sky looks blue because of the refraction of the blue light only.
Q. Which will reach the ground first : a bullet which is shot horizontally from a gun or similar bullet thrown upward from the ground ?
Ans. Obviously horizontally shot bullet is to come down first. Its direction is perpendicular to that of gravitational force. So both vector will not affect each other but in the case of a bullet shot upward has velocity vector in the opposite direction of gravitation force. So it will take more time.
Q. Why does an iron gain weight on rusting ?
Ans. The rusted iron is nothing but iron-oxide. Iron in the presence of moisture absorbs oxygen from the atmosphere and forms iron oxide. The weight gained is equal to the weight of oxygen absorbed.
Q. Why does hard water not readily form lather with soap ?
Ans. Hard water contains the sulphates and chlorides of magnesium and calcium, which form insoluble compounds with soap. Hence soap does not lather with hard water.
Q. Why are mountains cooler than plains ?
Ans. It is so because, firstly, the air on the mountains is rare than that on the plains and absorbs less heat than the air on the plains, secondly the heat absorbed during the day on the mountains radiates away more quickly due to the rarity of the air, thirdly, major portion of the mountains remains in shade.
Q. Why is sea-water saline ?
Ans. The rivers in the course of their flow and falling into the sea bring with them deposits of salt and this process has been going on for lakhs of years, it makes sea-water saline.
Q. Glass when heated cracks while metal does not.
Ans. Glass being bad conductor of heat only that part is heated which comes into contact with heat while the other parts remain unaffected. This results in unequal expansion and hence the tension which cracks the glass. On the other hand, metal is a good conductor of heat and so all its bulk gets uniformly heated and hence no surface tension.
Q. Why does it not hurt when we cut our nails ?
Ans. Nails are the parts of the body which are not connected either with the blood vessels or cartilage and hence having no relation with the nervous system. Therefore cutting them does not give pain.
Q. A hydrogen balloon rises. Why ?
Ans. Hydrogen is lighter than air, the weight of the hydrogen balloon is less than the weight of the air displaced by it.
Q. Why is a compass used as an indicator of direction ?
Ans. The magnetic needle of the compass due to the influence of the earth�s magnetic field always lies in the north south direction. Hence we can known the direction.
Q. Why is a country like Ladakh, it may be very hot in sunshine, but bitterly cold in shade ?
Ans. The atmosphere on great heights like Ladakh is rarefied, which offers little obstacle to the rays of the sun which are therefore, scorching. But the rarefied air absorbs little heat from the rays of the sun, therefore, the atmosphere remains cold. Hence it is very cold in the shade.
Q. Why does a straight stick look bent when a part of it is immersed in water ?
Ans. The rays of the light passing from a rare medium to a dense medium change their course due to refraction, where the rays coming from stick in water come in air at surface they get displaced away from perpendicular as our eyes see straight way so the stick seems bent.
Q. Why does water boil at a lower temperature on the hills than on the plains ?
Ans. The higher the pressure, the higher boiling point : the lower the pressure the lower the boiling point. The atmospheric pressure on the hills is lower than that on the earth.
Q. Why does a rider feel a tendency to fall when the horse starts running of stops suddenly ?
Ans. This is caused by inertia. When the horse starts running, the rider, being at rest, falls back. When a running horse stops suddenly, the rider being in motion has a tendency to fall ahead.
Q. Why does a person carrying a bucket full of water in his right hand bend towards the left ?
Ans. He bends towards his left so that the centre of gravity falls within the base. This enables him to keep up balance, otherwise he may fall.
Q. Why does tea cool more rapidly in a saucer than in a cup ?
Ans. In a saucer evaporation takes place more rapidly than in a cup. Cooling is caused by evaporation.
Q. Ice packed in sawdust does not melt quickly. Why ?
Ans. Ice packed in sawdust does not melt quickly, because sawdust being bad conductor, it cuts the heat rays.
Q. Why do you heat a metal rim before fitting it to a wheel ?
Ans. By heating, the rim expands and fits easily over a slightly bigger radius than that of the rim. On being cooled it contracts and has a firm grip on the wheel.
Q. Why do wet clothes dry slowly on a rainy day ?
Ans. On a rainy day the atmosphere air contains more water vapour than on a dry day and hence evaporation is slower.
Q. Why does a substance thrown up come to the ground ?
Ans. Because of the gravitational force of the earth.
Q. Why does moisture gather outside of a glass of cold water on a warm day ?
Ans. The temperature of the outer surface of glass of cold water is lower than that of its surroundings. The vapour in the surrounding atmosphere gets condensed on the outer surface of the water and appears in the form of tiny particles of water.
Q. Why are we advised to empty the ink from our fountain pen before going up on aeroplanes ?
Ans. A we go up higher and higher the air becomes rare and atmospheric pressure lower, so that the volume of the air inside the fountain pen will also increase and the ink will be pushed out thus spoiling the clothes and hence the advice.
Q. What happens to iron when it rusts ?
Ans. It reacts with the oxygen of the air and forms iron-oxide which is the rust.
Q. How would you distinguish between welding and soldering ?
Ans. Welding is the joining of metals by raising the temperature of the metals to fuse them together by metling their ends. Soldering is the joining of metals with the help of an alloy called solder.
Q. How does a ball which falls down, bounce up ?
Ans. It is due to the operation of Newton�s Third Law of motion. To every action there is equal and opposite reaction. A ball falling to the ground is slightly deformed. Due to the elastic force of the material of which the ball is made, the ball tries to recover its original shape. In doing so it forces the ground which pushes the ball upward due to reaction and the ball bounces up.
Q. An iron nail floats on mercury but sinks in water. Give reasons.
Ans. The specific density of iron is lower than that of mercury, hence it floats on mercury, while it is higher than that of water, hence it sinks in water.
Q. How do you convert Centigrade in to Fahrenheit ?
Ans. With the help of the following formula�
C/100 = F � 32/180
Q. It is advisable to work electric appliances when they are earthed suitably. Why ?
Ans. In case of short-circuiting, the current passess to the earth without harming the user, if an electrical appliance is properly earthed.
Q. How does a refrigerator keep food fresh ?
Ans. Food is kept fresh so long as fermentation does not set in; refrigerator prevents fermentation by providing low temperature.
Q. Ice wrapped in a blanket does not melt away quickly.
Ans. Blanket being bad conductor of heat prevents the outside heat from creeping inside.
Q. Why can a petrol fire not be extinguished by throwing water on it?
Ans. The heat of the petrol fire is so intense that the water thrown on it gets evaporated and decomposed. Hence it is not effective in extinguishing the petrol fire.
Q. A train stops when the chain is pulled. Why ?
Ans. When the chain is pulled, one small valve gets opened and air/atmospheric pressure is admitted to the under side of the piston head of the brake cylinder through pipe connections. Initially there is vacuum on both top and bottom side of the piston head. When the air/atmospheric pressure enters the under side of the piston head, the piston raises up due to difference of pressure and pulls the brake rigging to which it is connected with links and levers. Thus the brakes are applied and the train stops