(1) The Earth bulges out at the equator. Why?
This is due to the shape of the meth. The earth is not a true sphere but it is an ellipsoid. The equatorial diameter of the earth is 12756.27 km. While its polar diameter is 12713.505 km. the difference between its equatorial and polar diameter is about 43 kilometers. 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?
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: the 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 the skin, spotting of plants etc. that is why the ozone layer is necessary and essential for the animal as well as plant survival.
(4) The sky from moon appears black. Why?
Ans: as the moon lot no atmosphere, so the sky looks completely black when viewed from the moon.
(5) Roads are bent inwards on curves. Why?
Ans: The roads arc 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 center of the circle. When vehicles turn on a toed they fall outside under the influence of centrifugal force. In this way, there is a 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) Australia continent has winter season when we have a summer season in Pakistan Why?.
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, the southern hemisphere is inclined away from the sun and getting less direct rays. Thus the northern hemisphere has summer season and southern hemisphere has a winter season. Pakistan is in the northern hemisphere while Australia is in the southern hemisphere. So when there is winter in Australia there is the summer season in Pakistan.
(7) Meat takes longer to cook on mountains.
Ans: The meat takes a longer time to cook in the mountains because the atmospheric pressure decreases with attitude and the boiling point of a liquid indirectly proportional to the atmospheric pressure.
(8) Water remains cool in the 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 a 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 a 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.
Ass: In manual ice-cream making a mixture of salt and ice is always used because salt has the capacity to reduce the temperature of ice by decreasing its freezing point. That’s why ice and salt mixture is used as a freezing agent in manual ice cream making.
(10) It is not advisable to sleep under trees during the night. Why?
Ans: During the 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 the night.
11) Why the greenhouse 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, them 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 the summer season.
Why water boils quicker in mountains?
Ans: On Mountains, the pressure of the air is by due to height, as the air pressure decreases with altitude. In this way, water boils quicker on mountains at a temperature less than 100-degree centigrade, which is the boiling point °Now at ground level.
13) Rainbow is produced in the sky after rainfall and sunlight.
Ans: After the rain, many droplets of water travel in the atmosphere. When sun rays fall on these droplets, dispersion of water occurs and droplets act as a prism and produce s spectrum of seven colors. That’s why a rainbow is seen in the sky after rain.
14) Milk is considered as an ideal food.
Ans: Milk is considered an ideal food due to the following reasons: a) It contains all constitute of a balanced diet. b) Milk contains fat. c) Milk has high nutritional value become it contains proteins as well as minerals.
15) A lunar eclipse lasts much longer than a solar eclipse.
Ans: Lunar eclipse last longer than the solar eclipse because the length of the earth’s umbra’ 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) Goiter is common in hilly areas
Goitre is common in hilly areas because there is deficiency of Iodine in thc water.
17) Detergents are better cleaning agents.
Ans: A detergent consists of hydrophilic and hydrophobic ends. In case of din the detergent pushes the dirt off the wet surface of the Ibbric. The washing machine provides thc 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.
Decomposer break down organics into nutrients, which can be used by living organisms to
19) Places near the sea are cooler in summer.
Ans: Seawater keeps the temperature moderate. In the summer season, the places located near the sea are cooler due to the low temperature of water.
20) Colour blindness is more common in men than women.
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’. Ile will definitely bc co bur 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 colors absorb less heat, therefore, these are not heated as much as the black color.
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) Rainwater is more fertile than water from the tube well.
Ans: Rain water is more iertile because it contains many salts and nitrogen dissolved from the atmosphere.
23) The manhole covers are generally round why?
Ans: Manholes, which interconnect underground sewerage pipes, and serve as a point ofentry 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 o f 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 thc 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 the 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 falls in this pressure.
26) The image of a tree is inverted on t it, hank of a lake.
Ans: The water of lake actsees mirror. According to the laws of light, mirror forms inverted images.
27) Ps-neon 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 the 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 teourishment than ordinary boiled milk.
30) Bees die when they sting human being.
Ans: Their stingers arc actually ovipositors, tubular structures extending from the abdomen that sometimes contain eggs. When the barbed stinger is loft 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 sleepwalk?
Ans: Sleepwalk is a sort of disorder of sleep in which a person starts walking during his sleep.