➽ Why are telephone wires between two poles kept loose?
Answer: 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.
➽ X-rays penetrate through the flesh but not through bones. Why?
Answer: 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.
➽ What is a black hole? Why is it called so?
Answer: 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.
➽ Why do water pipes burst in severe cold winters?
Answer: 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.
➽ Most aircrafts and ships have their front shape pointed. Why?
Answer: 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.
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