Q4 of 10 Page 231

One light year is equal to _________.

i) 365.25 x 24 x 60 x 60 x 3 x 108 m


ii) 1x 24 x 60 x 60 x 3 x 108 m


iii) 360 x 24 x 60 x 60 x 3 x 108 m


(iii) is correct.

Explanation: A light year is the distance traversed by light in one year. So it is given by


Speed of light × No. of seconds in a year=


365.25 x 24 x 60 x 60 x 3 x 108 m


The no. of seconds in a year is given by the no. of days in a year ×no. of hours in a day × no. of minutes in an hour× no. of seconds in a minute.


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The Screw Gauge is used to measure the diameter of a _________ (crowbar, thin wire, cricket ball )

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One astronomical unit is the mean distance between the centre of the Earth and centre of the _________ i) Moon ii) Sun iii) Mars

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Correct the mistakes if any, in the following statements:

i) Astronomical unit is the mean distance of the surface of the sun from the surface of the earth.


ii) Light year is the distance travelled by light in one year in vacuum at a speed of 3x108m per minute.