Scientific Reasons From Past Papers 9

➽ Every fourth year has 366 days. Explain.

Answer: One revolution of the earth around the sun takes 356 days and 6 hours. But we consider a year as consisting of only 365 days and ignore 6 hours. In four years the difference becomes as much as 24 hours or one day. Hence, to every fourth year we add one day. That year of 366 days is known as leap year.

➽ Why are igneous rocks called primary or parent rocks?

Answer: Igneous rocks are formed when the molten material from volcanoes gets solidified. This material is liquid, hot and sticky which moves towards the surface through cracks and joints. All other rocks derived from these rocks. Hence, they are called primary or parent rocks.

➽ Why are the areas lying between the Arctic Circle and the North Pole in the Northern Hemisphere and the Antarctic Circle and the South Pole in the Southern Hemisphere very cold?

Answer: These areas are very cold because the sun does not rise much above the horizon. Therefore, its rays are always very slanting which emit minimum heat. These areas being very cold are called Frigid Zones.

➽ Why are the three hot regions of the world-equatorial forests, savannah lands and hot deserts-not found in Europe?

Answer: The three hot regions of the world-equatorial forests, savannah lands and hot deserts-are not found in Europe because Europe is the only inhabited continent situated entirely outside the tropics.

➽ Why is the lowest layer of the atmosphere in contact with the earth’s surface, the warmest?

Answer: The lowest layer of the atmosphere in contact with the earth’s surface is the warmest because the atmosphere is heated mainly from the below.