100 Important Scientific Reasons: Perspiring Man Feel Relief and Magnet Always Made of Soft Iron

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76) Why does a perspiring man feel relief when air flows by his side?

Ans: The air flowing by the side of a perspiring man quickens the pace of evaporation of perspiration from the body of that person, and the resultant loss of heat from his body causes the cooling sensation which provides relief to him.

77) Why is magnet always made of soft iron?

Ans: Magnet is always made of soft iron because ‘magnetisation’ and ‘demagnetisation’ both are possible in soft iron.

78) Why are telephone wires between two poles kept loose?

Ans: Telephone wires are kept loose between two poles so that they are protected from being broken due to expansion and contraction caused by the change of temperature in summers and winters.

79) X-rays penetrate through the flesh but not through bones. Why?

Ans:

  • The penetrating power of X-rays depends upon the potential difference between the cathode and the anode of X-ray tube.

  • The X-rays produced can penetrate through light element like flesh of human body but they are unable to penetrate through heavier elements like bones.

80) What is a black hole? Why is it called so?

Ans:

  • A black hole is a super dense planetary material formed due to the death of a star of mass more than five solar masses.

  • It is called black hole because any particle or photon approaching its surface is just swallowed by it. It appears black, as radiation is neither emitted nor reflected by it.

81) Why do water pipes burst in severe cold winters?

Ans:

  • Water freezes in pipes during winters, when the temperature goes below 0 degree Celsius (i.e., freezing point of water).

  • It expands and in the process exerts pressure on the water pipes, thereby sometimes bursting them.

82) Most aircrafts and ships have their front shape pointed. Why?

Ans: The shape of many objects, viz. aeroplanes, rockets, ships, etc. moving through air or water, are designed in such a way that friction can be reduced between the objects and air/water. Such type of body is known as streamlined and the process is known as streamlining.

83) An athlete runs some distance before taking jump, why?

Ans: An athlete runs a certain distance before actually jumping in order to increase his speed, and thereby, his inertia of motion. This increased inertia of motion enables him to jump a longer distance.

84) It is difficult to drown in the Dead Sea. Why?

Ans: The water of Dead Sea has a salt content of 27%. Therefore, its density is much greater than that of ordinary sea water and it also offers a greater up thrust. Hence, the body weighs less than an equal volume of Dead Sea water and is thus, able to float.

85) Why aquatic animals have soft skeleton unlike those of the terrestrial animals?

Ans:

  • The density of animals and fish living in water is almost the same as the density of water.

  • Therefore, their weight is almost completely balanced by buoyancy. That is why they do not need massive skeleton like those of terrestrial animals.

86) Why does a swimming pool appear less deep than it really is?

Ans:

  • When rays of light start from the bottom of a pool and travel from water to air, they are refracted away from the normal because they travel from a denser medium to a rarer medium.

  • As a result, a virtual image of bottom is formed above the bottom. Hence, a swimming pool appears less deep than it really is.

87) Why is electrical wiring in parallel better?

Ans: Electrical wiring in parallel is better because all the lines will have the same potential difference and if one line gets fused the other lines remain unaffected.

88) It is easier to swim in sea water than in river water. Explain.

Ans: The density of sea water is more than that of the river water. Therefore, the weight of sea water displaced by the swimmer is more. Thus, buoyant force of up thrust on the swimmer increases, making it easier to swim in sea water.

89) A cold compress is applied on the forehead of a person suffering from high fever. Why?

Ans: Evaporation causes cooling. As the water evaporates, it absorbs heat from the forehead and helps in reducing the temperature.

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