Give scientific reasons.
1) High and low tides are regular phenomena.
2) The value of ‘g’ at the center is zero.
3) In practice, the unit kWh is used for the measurement of electrical energy rather than joule.
4) Stars twinkle at night
5) Planets do not twinkle
6) We cannot clearly see an object kept at a distance less than 25 cm from eye.
7) Simple microscope is used for watch repairs.
8) One can sense colour only in bright light.
Answers
Answer:
1)the sea level on earth is directly influenced by gravitational force and due to gravitational force water on earth experience pull towards direction of moon hence there occurs high tide
2)Since, from Newton's law, we know F=mg. Since, mass m of an object can never be 0. Therefore, when F=0, then g has to be 0. Thus, the value of g is zero at the centre of Earth.
3)In practice, the unit kWh is used for the measurement of electrical energy, rather than joule. This is because joule is a very small unit and the energy consumption in day to day life is very large i.e. it comes in figures of 106 to 108.
4)In real Stars do not twinkle but as they are very far from the earth. So, they appear as point-sized sources of light and our atmosphere is largely heterogeneous having different densities and different refractive index. Due to these changing of physical properties, the amount of starlight reaching the earth changes from time to time and so stars sometimes appear brighter and at other times dull, which leads to the twinkling effect
5)Planets are not a source of light. Instead, they reflect low intensity light reaching them. ... As the planets are closer, planets appear larger in comparison to the stars.
6)We cannot clearly see an object kept at a distance less than 25 cm from the eye. This is because ciliary muscles of our eyes are unable to contract beyond certain limit.
7)A simple microscope is used by watch repairers because,a magnification of about 20 times is obtained by the convex lens of small focal length used in a simple microscope. Therefore, it is used by watch repairers to see the minute parts of the watch clearly without causing any strain to the eyes.
8)The cells present on the retain and responsible for colour vision are known as cone cells. These cells become active only under bright light and remain inactive under dark. Thus, we are able sense only in bright light.
Explanation:
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