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Old Friday, November 11, 2011
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Roshan wadhwani Roshan wadhwani is offline
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SCIENTIFIC REASONS FROM PAST PAPERS (95 To 2011):


1) The Earth bulges out at equator. Why?

Ans: This is due to the shape of the earth. The earth is not a true sphere but it is an ellipsoid. The equatorial diameter of the earth is 12756.27 kms. While its polar diameter is 12713.505 km. the difference between its equatorial and polar diameter is about 43 kilometres. The rotation of the earth on its axis produces a centrifugal force which increases its equatorial diameter. That is why earth bulges at the equator.

2) The Sun appears red at sunset and sunrise. Why?

Ans: The sun appears red at the time of sunset and sunrise due to the scattering of light by small particles of dust or smoke near the surface of the earth. The light travels relatively without hindrance that is why the sun appears red at the time of sunset and sunrise.

3) The ozone layer in the atmosphere is necessary for our survival. Why?

Ans: ozone layer in the atmosphere is very necessary for plant and animal survival because it is the absorber of ultraviolet rays which are very dangerous for animal health. Ultraviolet rays cause cancer of skin, spotting of plants etc. that is why the ozone layer is necessary and essential for animal as well as plant survival.

4) The sky from moon appears black. Why?

Ans: as the moon has no atmosphere, so the sky looks completely black when viewed from the moon.

5) Roads are bent inwards on curves. Why?

Ans: The roads are bent inwards on the curves and at the turns because the bents avoid falling outside and prevent the accidents.
OR
When an object turns in a circle it is influenced by a centrifugal force which pushes it away from the centre of the circle. When vehicles turn on a road they fall outside under the influence of centrifugal force. In this way there is danger of falling or slipping out of road at a turn. Roads are made in a way that these bent inward at the turns to avoid falling outside and to prevent accidents.

6) Australian continent has winter season when we have summer season in Pakistan.

Ans: the earth on its axis is not at a vertical angle to its orbit. It is inclined at an angle of about. In this way when the northern hemisphere of the earth is inclined to the sun and getting direct sun rays, southern hemisphere is inclined away from the sun and getting less direct rays. Thus the northern hemisphere has summer season and southern hemisphere has winter season. Pakistan is in the northern hemisphere while Australia is in the southern hemisphere. So when there is winter in Australia there is summer season in Pakistan.

7) Meat takes longer to cook on mountains.

Ans: The meat takes longer time to cook on the mountains because the atmospheric pressure decreases with attitude and the boiling point of a liquid is directly proportional to the atmospheric pressure.

8) Water remains cool in earthen pitcher.

Ans: This occurs due to the process of evaporation. Water gets cooled on evaporation. As the earthenware pitcher is concerned, they have small pores. Water tends to come out of pores and evaporates which results in cooling effect on the earthenware and water.
While in the metal pots there are no pores and evaporation does not take place. Besides metal has tendency to absorb heat that why water does not get cooled in a metal pot.

9) Ice and salt mixture is used as a freezing agent by manual ice-cream makers.

Ans: In manual ice-cream making a mixture of salt and ice is always used because salt has capacity to reduce the temperature of ice by decreasing its freezing point. Thatís why ice and salt mixture is used as freezing agent in manual ice cream making.

10) It is not advisable to sleep under trees during the night.

Ans: During night the plants release carbon dioxide (CO2) which is a poisonous gas and injurious to health. That is why it is not advisable to sleep under trees during night.

11) Why the green house operators paint their glass roofs white in summer?

Ans: White colour is the reflector of light and it absorbs less heat as compared to other colours. As in summer there is already very hot season and heat is not required to that level. That is why the green-house operators paint glass roofs white in summer season.

12) Water boils quicker on mountains.

Ans: On Mountains the pressure of the air is low due to height, as the air pressure decreases with altitude. In this way, water boils quicker on mountains at temperature less than 100 degree centigrade, which is the boiling point of water at ground level.

13) Rainbow is produced in the sky after rainfall and sunlight.

Ans: After rain, many droplet of water travel in the atmosphere. When sun rays fall on these droplets, dispersion of water occurs and droplets act as prism and produce a spectrum of seven colours. Thatís why a rainbow is seen in the sky after rain.

14) Milk is considered as an ideal food.

Ans: Milk is considered as an ideal food due to following reasons:
a) It contains all constitute of balanced diet.
b) Milk contains fat.
c) Milk has high nutritional value because it contains proteins as well as minerals.

15) Lunar eclipse last much longer than solar eclipse.

Ans: Lunar eclipse last longer than the solar eclipse because the length of the earthís umbral shadow cone is more than three times the average distance between the moon and the earth, so the shadow is relatively wide at the point where the moon crosses it.

16) Goitre is common in hilly areas.

Ans: Goitre is common in hilly areas because there is deficiency of Iodine in the water.

17) Detergents are better cleaning agents.

Ans: A detergent consists of hydrophilic and hydrophobic ends. In case of dirt the detergent pushes the dirt off the wet surface of the fabric. The washing machine provides the agitation.

18) Decomposers are important for life.

Ans: Decomposers break down animal waste and dead organisms in order to get energy and release free nutrients back into the ecosystem.
OR
Decomposers break down organics into nutrients, which can be used by living organisms to create new life.

19) Places near sea are cooler in summer.

Ans: Sea water keeps the temperature moderate. In the summer season the places located near sea are cooler due to the lower temperature of water.

20) Colour blindness is more common in men than women.

Ans: Women have the sex chromosomes XX, while men have the chromosomes XY. The gene for normal colour vision is found on the X-chromosome. If a woman has one X-chromosome with the gene and one without it, she will not be colour blind. On the other hand, a man with an X-chromosome that is missing the gene has no 'backup'. He will definitely be colour blind. Colour blind women have both X-chromosomes missing the colour vision gene. This is less probable mathematically than having just one X-chromosome missing the gene.

21) Light colours absorb less heat therefore these are not heated as much as the black colour.

Ans: Dark colours do not exactly absorb more heat, but they do convert a higher percentage of light into heat. In the sun with a dark coloured shirt it gets hot, where a lighter coloured shirt would not get nearly as hot. This is due to the amount of light being absorbed by the colour. The lighter the colour the smaller is the range of visible light being absorbed and converted into heat. White objects reflect all visible light, where black objects absorb all visible light.


22) Rain water is more fertile than water from tube well.

Ans: Rain water is more fertile because it contains many salts and nitrogen dissolved from the atmosphere.

23) The manhole covers are generally round.

Ans: Manholes, which interconnect underground sewerage pipes, and serve as a point of entry for cleaning the pipes, are located at every major sewer pipe junction, and are capped with round manhole covers. The reason for the circular construction of these covers is, quite simply, that covers of any other shape would fall through the manholes by virtue of their varying diameters. Circular manhole covers do not vary in width, or in diameter, as is the case with these other shapes, thus remaining in place despite the street traffic running roughshod over them.

24) Clothes of a moving dancer bulge.

Ans: The clothes of a moving dancer bulge outside due to the centrifugal force which tends to move away from the centre.

25) People are advised not to stand near fast moving train.

Ans: One should not stand beside a fast moving train because of the strong pressure of air which carries along. A man can fall in this pressure.

26) The image of a tree is inverted on the bank of a lake.

Ans: The water of lake acts as a mirror. According to the laws of light, mirror forms inverted images.

27) Polar star is always seen in the north.

Ans: It is because the Polar Star (North Star) is closest to the location of the celestial North Pole.

28) We never see birds urinating.

Ans: The birds do not have a urinary system like other living beings which possess urinary excretory organs. In the birds the urine is excreted from body without special organs.

29) Pasteurized milk has more nourishment than the ordinary boiled milk.

Ans: Pasteurized milk is obtained by heating milk at a temperature of 60 degree Celsius for 30 minutes. In this way the TB bacteria are killed without damaging the milk protein. Thus pasteurized milk has more nourishment than ordinary boiled milk.

30) Bees die when they sting human being.

Ans: Their stingers are actually ovipositors, tubular structures extending from the abdomen that sometimes contain eggs. When the barbed stinger is left inside the victim, the honeybee mortally tears her abdomen in the process. They leave their stingers in the wound with a tiny venom sac attached. Fortunately, only about one out of a hundred people are allergic to bee sting, but allergic reactions can be very serious.

31) Cloudy nights are usually warmer than the clear ones.

Ans: The clouds serve as a barrier and prevent the loss of heat. Thus the warm temperature is maintained.

32) Why do some people snore?

Ans: Some people snore during their sleep because the breathing action produces sound. This is so because the pharynx or the windpipe offers resistance to the air taken in or expelled.

33) Why do we sometimes sleep walk?

Ans: Sleep walk is a sort of disorder of sleep in which a person starts walking during his sleep. The sleeper walks and performs complex activities automatically without regaining consciousness.

34) Climbers bend forward while climbing mountain.

Ans: While climbing a mountain, a climber bends his body forward in order to keep the centre of gravity of his body within two thirds portion. According to this principle the Pisa Tower is not falling.

35) Why climbers get their food by climbing on other trees?

Ans: The climbers are mostly parasites and they cannot manufacture their food. Therefore, they climb on other trees and get food from them.

36) Mars is called red planet.

Ans: Mars is called the red planet because its colour is red due to the desert like surface.

37) Vitamin D is the essential component of the body.

Ans: Vitamin D is necessary for body because it is essential for bone formation and retention of calcium in the human body. Vitamin D also protects the teeth.

38) The weight of the object is less at the equator than at the poles.

Ans: The weight of an object is the product of mass and force of gravity. The equatorial diameter is more than the polar diameter. Thus, the force of gravity is more at the poles and the weight is more there.


39) The dogs pant, the birds open their mouth and the elephants move rapidly their ears.

Ans: All of them do not sweat; they use the above mentioned mechanisms to cool themselves.


40) A geostationary satellite appears standstill to a viewer on the equator of earth.

Ans: Because the distance remains the same.

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